Audi S3

The engine is the most underestimated part. On paper it is the A3's block, but nothing above it is the same. A workshop that has done timing chains on an A3 has not seen this turbocharger, and the parts do not interchange.

American S3s are widely run on tuning software, Stage 1 or 2. Cars often arrive at auction having been used hard, and the software does not show in photographs. Check the chain and the turbo's condition before bidding, not after delivery.

Suspension is the next cost. Most cars carry adaptive magnetic dampers. One genuine unit costs what four ordinary A3 dampers cost, and converting to conventional springs removes the reason the car was bought.

The nose hides more than it looks. Calipers and discs are larger and dearer, and behind the bumper's side grilles sit extra radiators for the engine and the gearbox. In a frontal impact those are exactly what the breakers do not have.

The gearbox is a wet-clutch S-tronic, six or seven speeds. It takes launch control, but wants fluid every 40,000 km. Neglected, a mechatronic repair starts in four figures.