I am very familiar with a vendor who does this.
I can tell you that these guys know a LOT about engines, and had to put a LOT of work into the R & D to make some production engines. Don't forget that these pretty much *have* to be made from castings, since the coolant passages are quite difficult (impossible?) to machine. It probably took a half a million dollars in R & D to make the first block, including the casting pattern. Once you have a pattern that works, the next ones will obviously be much cheaper. Of course after the blocks are cast, there is a lot of machine work.
And that is just for the blocks...
-Bob C.