I reckon you could get about 92bhp out of the 1.2 8v without spending more than about £500
1.1-1.28v 75bhp engine ~£200 (gearbox is the same as are engine mounts I think), that price would include ecu/fuelpump/fuel regulator etc
34mm to 43mm throttle body bore by tricker ~£90
GSR induction kit and big ass plenum and you need a cinq 899cc or 1.1 'bob' ~ £120
used supersprint or similar manifold and down pipe, the rest you can get in time, start at the manifold.
that lot coupled with a near complete engine rebuild (which doesn't take that long especially when on the previous day some scrotes stole your tools
), and a rebore/hone etc and a quick head rebuild (maybe a bit of polishing can be done here if you have the patiance) should give about the 90bhp mark.
See pandamonium's website for more info on how to get circa 115bhp out of the 1242cc (hot cams and a ceromonial dumping of all things electrical and injectionated to be replaced by some fair sized downdraught carbs:slayer: )