budget for 10k on a decent bottom end with the top end being freshend up, you'll get cheaper prices but by them time its finished it will be usual be around that figure, the most important part is finding someone who will stand by their engines and warrent them if anything goes wrong, i knew a forged rb25 that lasted 7 years saw lost of limter, was taken to the strip almost evey weekend, hundereds of dyno runs, in the end it only lost a bit of oil pressure running an n1 oil pump and making between 350 to 400rwkw, on the other side i have built motors last less than 1500km's