heres my rule of thumb, for a fun cossie that is relaible and really enjoyable...

these are the prices i think for each car with around 400bhp no welded etc

a
saph
2wd £7000-9000
4wd £9000-£11000

3 door cosworth £13000-£15000

escort cosworth £20000-£22000

if you buy a cosworth for less than these prices you will end up spending loads on it and it will total these amounts..

unfortunaly people seem to chop up the good ones and sell all the parts so you may have to build a good one your self...

this prices are from my experiance..