Homemade Ghostlops are $130-150. Should be about the same for any homemade cart. Diggerman is probably a hack. If legit, it would be from FACE, the makers of Gururin, but judging from the game itself, I think it's a hack. Probably a fancy Asian one. Much of the game, even the music is boosted from Gururin, and the game isn't all that fun but it's one of the classic hacks that's been out there for a while, and it does play as a full game I suppose.
Billy's page is wrong. I price the game on my guide for about $300, it is the rarest officially released MVS cart. I got mine from Ebay UK for less than $200 because it had been bastardized with a "Bang Progress" label. It has legit boards, and I've since relabeled it.