The chasis will rust if not treated properly and waxoyled. My tuscan is 8 years old and has surface rust after just 20k miles! It will cost me £400 for the garage to take the body off and rub the whole chasis down spray and waxoyle. On the Chimera and Griff its the out riggers that can rot and you have to take the body off to have a look. It can be a DIY job as long as you have the space.
I used Rob Ingleby to check over my tuscan, he has been looking at TVR's for people for over 8 years, he either does a finding fee in that case he will do what Jurgan does and find a car in your budget, check it over and test drive it for you as well as negociate a price. Or you can just pay him to look at a car you have seen on pistonheads/auto trader.
His site is http://www.findasportscar.co.uk/