alright, i'll weigh in here, in COST, including label, donor, and eproms, SNES repros run from $15-30
thing is, there's a lot of extra work, trimming wires, rerouting, etc.
if you want to do it via TSOP, the cost is pretty much set at $20, with no rewiring, depending on how you do it.
thing is, that way is actually quite a bit more difficult, as TSOP chips are a pain.
so either way, it's a lot of work, but i'd tell ya to just go back and change something like SNES Super Scope 6 or madden 95 into the game, rather than messing with the SFC carts, that way if you screw up your first couple (chances are you will) then it won't be a big deal.
here's the basic way of doing a 4 eprom SNES repro:
