I figured 3 months actually, and 1 month extra in case anything unforeseen.
I'd figure more than 1 extra month based off how PCE projects usually go.
$5000 is insanely cheap, but I'd do it for the challenge and the love of coding for PCE. $5000 would pretty much just pay the bills, while I would concentrate full time on such a project.
If you're doing it for the love of PCE/the challenge, you wouldn't need the money.
This is a terrible idea, and I can't see people actually ponying money up for it. Also, your previous work repertoire doesn't really guarantee this 4 month turnaround time you've come up with.
If you really want to see it done, why not just do it for shits and giggles, for the "love and challenge", instead of basically asking a bunch of people to give you 5000$ for a game we could all already play. It's not like it's a monumental task to locate a SuperGrafx and one game for it. It's also more productive, since you now have a new NEC console with some other games worth playing.
Unless you plan on asking 5000$ a pop to convert the entire SGX library to PCE.
Do enough people here even lack a SuperGrafx + Daimakaimura? I don't think there are 50 active members here, let alone 50 active members who don't already have a way to play this game.