Get a 406 Coupe with 2.2 HDi diesel unit - second user 2002 models well under £7k. Factory tune is 136bhp. Bung three hundred quid to Celtic (
www.celtictuning.co.uk) and receive an ECP remap in return. Shoves out about 180bhp with torque over 300lbft. Run it on BP Ultimate Diesel and get a few percent more for the premium.
Keep the other £2700 in hand for front tyres, but allow a couple of quid for the extra insurance premium, because, you're going to declare it, of course, aren't you?
Seriously though, the 2.2 with a remap is a remarkable piece of kit. 0-62mph can be done in about 8 seconds if you're gentle with the clutch/rubber.
50-70 in fourth is stupidly quick, it in the jaguar XK8 / Boxster league. And; yes, I've driven a couple of them.
Rgds,
P.