mikep,
does anybody know if i could put it on to a PFA permit for personal flying
No - you can't have certified aircraft on a PFA permit.
I can't help you with any of the other stuff - the how much will a C of A cost is very much a 'how long is a piece of string' question: it depends on what need doing to the aircraft. I also have a sneaking suspicion that there's a spar life limit on the PA-38, although I don't know how many hours it is (10,000 rings a bell though).
Try doing a forum search on PA 38
Brooklands