Someone will probably have $2,000 at a minimum in a build like that giving them the benefit of the doubt of assembling it themselves. And that depends on how deep into the heads the machinist traveled. they could have upwards of $1,000 in the heads alone depending on how nuts they got with machine work and replacing parts. (new valves, springs, retainers, locks, seals, etc.) And machine work and replacement parts on the block would be probably in the neighborhood of 1,000ish as well. If they have receipts to prove all the work and parts then $2,000-$3,000 isn't out of the question. IF it all checks out. The heavy duty 4 bolt 454 block alone in my truck, my buddy at the engine shop wanted to give me $600 for the bare block and give me a 2 bolt replacement block to build off of because "that block is really desirable and you don't need a 4 bolt for what you're doing". Of which he added that since I had it, it would make the best foundation to start with. (some may remember my truck started it's life before me as a cheater class pulling truck so it had good parts to start before I rebuilt the engine.) So depending on what he's got it could get pricey quick. But it's all worth what someone is willing to pay. But buyer beware, because quite frankly lots of "fresh" engines listed on for sale sites are simply "DuPont overhauls" that merely look fresh.