It depends on your budget and taste in cars, really.
If you're looking to capture the spirit of something that's been competitive in the last three decades, then you're going to need a budget of at least £50k, probably more -
http://www.kitcarlist.com/race-cars.html
If you like the classics from the 50's and 60's then you have more choice and could build a Tribute D Type to a high standard from around £6k, which would give you a stunning car that will turn far more heads than a 500bhp modern looking racing car.
Take a look at Mick O Malley's Ecosse Blue example to see what's possible (not sure what his budget was, though) -
http://www.madabout-kitcars.com/foru...ead.php?t=6083
If you have a bigger budget, then circa £30k could just about get you into a GT40 or Suffolk C Type, and maybe another £10k for a Ferrari P4 (not sure if anyone's still making them).
If you're prepared to look at cars that competed in lower classes over the years then that gives you other alternatives, such as the Le Mans Spitfires, which you should be able to get on the road for around £12k -
http://www.triumphspitfirelemans.com...ocument&part=4
Then there's the panel kits which effectively add a body kit to a recent production car to make it look like something different, which could see you with a Tribute GTO or 250 SWB for as little as £10k, or a Nu Dimension 911 GT3 RS for under £15k -
http://www.anudimension.com/index.html
And finally, given your skills and experience, you could always build your own car from scratch. There was someone on here building an all aluminium Ferrari P4 (could've been a racing Dino) but I can't find the thread.
Good luck finding something that will keep you amused.