Don't feel bad, I did the same thing a few months ago (only much worse...lol) when my betta was sick and got flamed to death about keeping him in a bowl. Anyway, long story short, he died and I sort of blew up at everyone who was rude and left for a few weeks... as you can see I couldn't resist coming back.

I'm only a year younger than you and I totally understand where you're coming from on this issue. My parents have almost totally stopped paying for my fish stuff, and if I were you (or your dad) I wouldn't be very inclined to pay $100 for anything fish related. (LOL, I always get the same thing "It's your money." now THAT'S pressure!! haha) Now I do like the 50/50 idea, but 60/40 may end up being better since that's what your dad first wanted to pay (in the $30-$40 range). BTW, you should probably wait anyway until your 10g is running smoothly, so if you miss this (pretty great) deal there's always another one coming (especially with something like craigslist... you may even find a better one!).

I'm not sure if that was any help at all, but good luck with your fishkeeping endeavor.