The supercar has been a struggle to sell, which means potential bargains for interested buyers.

Among the more exotic niches of the car business is the marketing of supercars.

The cars, which carry price tags in the mid-six figures, require a tricky marketing balance. If they become too scarce, speculators move in, driving up prices and making the cars unavailable to enthusiasts. But if too many examples show up on the market, they lose the appeal of scarcity and potential buyers move on to the next big thing.

Consider the case of Mercedes’s SLR McLaren. Based on its spec sheet, the car should have been a home run when it appeared in 2004. It had a supercharged V-8 engine that put out 617 horsepower and got the car from zero to 60 mph in 3.6 seconds; its top speed was 207 miles per hour. It sported an advanced carbon fiber body and retro scissor-style doors. The SLR also had a history behind it. It was said to have been inspired by the Mercedes 300 SLR of 1955.

But the market for supercars was weakening when the SLR came out, and the car received some middling reviews. There were complaints about its styling and its function — whether it was really a sports car or a grand tourer in disguise. Mercedes had planned to sell 500 SLRs a year at $495,000 each, but after 2005, it wasn’t able to achieve that goal. It ended production of the car in 2009 — two years ahead of schedule.

Today, the SLR is unloved and unwanted. According to one dealer, there are currently 26 unsold cars at the port in Los Angeles. Based on last year’s selling rate, that would be a three-month supply. A Mercedes spokesperson says that number is too high — she says “only a handful of SLRs are there” (though there may be more in East Coast ports).

If you want to buy an SLR for Christmas, now is the time for a bargain. Mercedes says that if you group all the wholesale and retail dealer allowances together, you could knock the price down by $175,000. A dealer says the number is actually higher: $250,000 off the sticker.

But if you think the SLR has become damaged goods, never fear: a new Mercedes supercar is on the way. The 2011 SLS AMG, introduced at the Frankfurt Motor Show in September, gets a 571 horsepower V-8 that will fling the car to 62 mph in 3.8 seconds, with a top speed of 197 miles per hour. In addition, it has genuine butterfly doors. The estimated price is $225,000 or less than half the price of the SLR.

Caveat emptor.

The red-over-black GT-R squatted in my driveway like an angry beast from another planet. No graceful shapes or elegant curves disguised its blunt purposefulness.  This is the car designed, first and foremost, to beat all other production models around Germany’s famed Nürburgring.  Whether it does or not, it lives up to its nickname “Godzilla” even when parked.

Which would be fine, except that I live in northwestern Connecticut, and, despite the proximity of Lime Rock Park (“Roadracing capital of the East”), I almost never get an opportunity to evaluate the full potential of a 480-horsepower car that can claw its way to 60 miles an hour in 3.9 seconds (without launch control) and claims a top speed of 195 miles per hour.

What I could do was make some short loops around town and then log 150 miles at higher speeds on the Massachusetts Turnpike. What I found was that this is not a car you would choose to make a leisurely morning run for the New York Times and a cup of coffee.  That’s mainly because first gear in an all-wheel-drive car with the power of the GT-R has all the subtlety of a stump-pulling tractor, heaving and jerking as it translates the immense horsepower into forward motion.  Second gear in the dual clutch, paddle-shift, six-speed transmission was lots smoother,  but you needed to get up a little speed before the computer brain behind it would allow you to get there.

Nor does the view from the driver’s seat give you much to warm up to.  The cockpit has all the ambiance of an F1 racer, with surfaces and instruments designed more for practicality than esthetics, purpose  not pleasure. This is not a car for lounging in.  One thoughtful touch is the addition of two rear seats, suitable for pets, small children, and masochistic adults – an unusual  concession to practicality.

But although the GT-R is designed to be a daily driver and carries a relatively modest sticker price of $72,000, it is as finicky in some ways as an exotic.  Specifically, the alignment tolerances are so narrow that a minor irregularity can throw the wheels out of whack.  My GT-R shimmied regardless of the road surface, requiring constant corrections of the steering wheel.  I was informed that it needed a wheel alignment after only a few thousand miles of use.

With those caveats, the GT-R lived up to its advance billing as one of the most technologically-advanced,  high-performance cars in the world and is ably performing its task of raising Nissan’s profile. GT-R owners form a very exclusive club – the purchase of only 321 cars was transacted in November, but enthusiasts have gone bonkers over it and Motor Trend voted it car of the year. For me, however, the GT-R is a car more to admire than to love.

A two-seat convertible like the 911 Turbo Cabrio that accelerates to 60 miles per hour in four seconds and carries a sticker price of $154,050 would seem like an irrelevance in these days of $4 gasoline and difficult economic times.

Porsche 911 Turbo Cabriolet

It is – except to two important constituencies: Porsche and its customers. Against all logic, the 911 line of rear-engine sports cars continue to be the most popular Porsches, outselling the less-expensive Boxster two-to-one. As the most expensive 911, the Turbo Cabrio thus becomes the flagship of the Porsche brand and an aspirational target for its buyers. If you are dying to have a Porsche, you might as well pop for the top of the line.

The “arctic silver metallic” car I drove recently effortlessly satisfield both parties. It is one of the most strikingly handsome cars on the road, with a tailored front-end, bulging rear flanks, and tasteful spoiler far more refined than those on earlier turbo models. The descriptive “whale tail” no longer applies. Inside, the black full-leather interior was purposeful, rather than indulgent, and Porsche is making strides by improving the appearance and utility of its interior controls (though you would never mistake them for a Lexus). The one-touch convertible top, which stows neatly in the rear deck, operates efficiently and unobtrusively.

The big surprise comes when you get behind the wheel, because the Turbo Cabrio is as comfortable as a well-worn leather glove. It is one of those rare super cars that is equally at home running errands as it is accelerating through the gears. The pedals operate easily, the shifter on the manual gearbox is a model of balance and performance, and the steering wheel responds to the most subtle of inputs. Once you get used to finding the ignition switch on the left hand side of the steering wheel (for those running Le Mans starts), it functions effortlessly as a daily driver. And at 15 miles per gallon city, 24 mph highway, the mileage isn’t horrible.

With its 480-horsepower engine revving at full throttle, the Turbo Cabrio is capable of scary high speeds, but you won’t find an analysis of its top-gun handling characteristics here. Absent hot laps on a race course or avoiding the police on some deserted highway, the Turbo Cabrio possesses performance capabilities that will be infrequently accessed by its owners. But that doesn’t prevent Porsche from charging top dollar for the car – or from its owners paying it. Both parties can feel they have exchanged fair value.