s**t, I understand you a bit more, I'd be a lunatic with 9 kids as well lol. I was going to suggest sickbikeparts for the 4g, they had a few older ones with the solid 100t pulley and 12t output freewheel for $70, but those sold out quick.
Is your current transmission a belt or chain drive? If it's the cheaper belt drive then it'll work better than the even cheaper chain drives, because belts don't stretch like the chains do. It also has a 5:1 reduction. The single chain trannies do not have near enough reduction (3:1) and it has no outboard bearings for the shafts, so they fail prematurely. The double chain has enough reduction (5:1) and outboard bearings, but that chain is a pos.