The Mk2 R5GTL is 1400cc so go for a 1100/1300cc model TL TR TS. There's always plenty on Ebay. MK1's in really good condition are difficult to get hold of.
So, go for the smaller engined MK2 and the more money you pay, the better the car will be. I have seen plenty of one owner low mileage examples go for under £800 on Ebay.
By the way, GTL means a trim pack and not extra performance!!!
Good luck