really depends upon spec, if you just want a standard rebuild and your engine doesn't need much machining work then it could cost 350 in parts and another few hundred for labour so £500,

However, if it has badly worn bores, worn crank journals, a knackered cam (and probably a worn oil pump) etcetc. You would be looking at £800 in parts alone for a standard(ish) build.

I would always recommend having a reputable place blueprint, balance and build your engine, and as a very minimum you should install ARP con rod bolts.

Good luck

Rob,