If you were in any doubt that cars are getting cheaper, then consider this: in 1996 a new BMW 850Ci cost £83,000; today its replacement, the BMW 650i Sport, costs £56,000.

But the really good news for used car buyers is that a two-year-old 6-series can be picked up for little more than £40,000. In the land of luxury grand tourers that’s one of the biggest bargains around.

Introduced to the UK in March 2004, the 6-series was initially available with just one engine, a 4.4 litre V8 producing 333bhp, badged the 645Ci. But thanks to a relatively low kerb weight of about 1,650kg it could sprint from 0-60mph in less than 6sec and still be pulling like an express train when it hit its artificially limited 155mph top speed.

Last year this engine was phased out and replaced with a larger 4.8 litre unit producing 367bhp badged the 650I, but these are still rare on the secondhand market. However, there are plenty of the entry-level 3 litre six-cylinder versions, the 630i, that joined the range in 2004 and could hit 62mph in 6.5sec even with a relatively modest 258bhp.

In November 2005 BMW introduced the top of the range M6. With 10 cylinders and 507bhp it reached 62mph in just 4.6sec. Despite this ferocious performance and the fact that it was the most expensive in the model range, the M6’s price tag of £82,605 was still less than the price of that 850Ci from more than a decade ago.

The BMW 6-series is a car that will get you noticed. From the front it has enormous road presence, especially with headlights blazing. From the side it mixes 7-series tail with 5-series middle and Z4 front. Somehow the combination works and the result, if not quite a thing of beauty, certainly commands respect.

Open the large doors, slip behind the wheel and many drivers will be surprised by the reverse Tardis trick that BMW has played: the car may look big on the outside but that is not reflected inside the cabin. In particular, space for rear passengers is limited.

Happily, at 450 litres the boot space is more generous, especially as you will probably only need to pack for two.

It is on the road that the 6-series comes into its own. Close to perfect weight distribution means you can push the car hard with complete confidence, safe in the knowledge that, if you need them, traction and stability control systems will intervene.

If you can, find a used example with the optional Dynamic Drive system that automatically adjusts the suspension so the car remains flat through the corners. It levels the ride to such an extent that you will need to check your speedometer to keep any sense of just how quickly you are travelling.

In fact, if there is a complaint it’s that the 6-series is simply too clinical to be regarded as a true driver’s car. The only additions that stop it from being magic-carpet smooth are larger alloys and sports suspension.

The biggest problem with the 6-series is the huge choice facing potential buyers. First they must select the engine, then choose from manual, auto or SMG gearboxes, which are available on all but the M6 version, and then they are still left with a lengthy list of colours, options and interiors.

The general rule as far as colour schemes go is to stick with classic blues, blacks and silvers. Never opt for a light interior and light exterior (the combination always looks naff) and it hardly needs to be said that there’s no point in paying for options that you would not have chosen yourself when new. Naturally a service history should be impeccable, with receipts as evidence of the work carried out.

When you check out the classifieds you should find that there are plenty of examples vying for your cash, so remember to haggle hard.

BMW iDrive

Not the most instinctive system to control sat nav, climate and entertainment, but with practice you should be able to master it

Tyres Check inner edge of front tyres for uneven wear

Seats Check sides of driver’s seat for wear on high-mileage cars

Servicing Controlled by the onboard computer so intervals can vary dramatically depending on driving style

Parking aid Audible and visual parking display is among the best on any car

Economy Better than many buyers might expect; even the V8 should achieve about 23mpg in mixed motoring

Head-up display Optional system projects road speed on the inside of the windscreen

Boot space A 450-litre boot with additional benefit of folding rear seat

Security Factory alarm and immobiliser as standard but some insurance companies may insist on an additional tracking device

Vital statistics

Model BMW 645Ci

Engine 4398cc, V8

Power 333bhp

Transmission Six-speed manual

Fuel 24.6mpg (combined)

Acceleration 0-60mph: 5.6sec

Top speed 155mph (limited)

The one to buy

BMW 645Ci manual 2004 04 with 40,000 miles. Pay £31,250 at a BMW dealer or £29,000 privately

Values Mileage 10,000 20,000 40,000 2004 04

Trade £29,450 £28,400 £26,450

Retail £34,250 £33,250 £31,250

2005 05 Trade £32,800 £31,600 £29,400

Retail £37,500 £36,250 £34,250

2006 06 Trade £40,600 £39,000 £36,300

Retail £45,750 £44,250 £41,500

Or for similar money

2000 X Aston Martin DB7 coupé

2004 54 Mercedes-Benz CL 500 coupé

2004 54 Maserati 4200 GT coupé

2004 54 Jaguar XKR coupé

2005 05 Lexus SC 430 coupé