If you had to buy all the bits and have it built I bet you would be in for over £10k (maybe more quite a bit more) but a second hand engine is hard to price. I once offered someone about £5k on here for an engine advertised for £7,500 and he got the arse saying I had offended him....I tried to explain that an offer is better than none at all.

Unknown, old and standard engines can go for over £3k.

If I bought it I would want someone like Mark Shead to strip it and check it then put it all back together for peace of mind unless it was a known company builder and they are willing to put their name to it being a good engine. It's a lot of money if it breaks.