as apparently you live round the corner I can save you some time and lend you a copy of it.
The short version of that book is you can pick up an old ford (newer version uses a sierra as the old car is rare as hell these days) and almost build one for around £400 add another couple of hundred if you want it to be road legal in the UK as it now has pass through something called the Single Vehicle Approval (SVA) test which came in to force a couple of years back.
If you actually want a decent lotus 7 style car on a minimal budget I can highly recommend Robin Hoods based on the 2B series:
http://www.robinhoodsportscars.com/index.phpYoure looking around £3.5k by the time youve got the kit and sierra. But its a damn fast car for the money and great fun.