also consider a newer 106gti or saxo VTS, not the cult status of the 205 but still excellent handling and does that 3 wheel trick round corners too!

Pretty straight forward to to tweek it upto 150bhp and if u wanted to go serious there supercharger kits and turbos available to get upto 300bhp!

On the other hand, you could pick up a £100 citroen AX - 650kgs as standard and fit the 106gti engine in, very easy swap as its the based on the same TU block. Just with standard stuff your looking at 200bhp/tonne with that! Ive done about 5 of these conversions and have never had any reliability issues.