@thenomain I think the first question would be to ask yourself what you're doing it for; either you're a professional getting paid, or you're a hobbyist making a buck on the side.
If it's the former then you need to be paid the usual way; market price for your time investment. That means having a contract, a deliverable goal set in advance, a timetable, and as little maintenance after as possible; this is where many coders for hire realize they got screwed, when they spend twice as much on a project that's over implementing "oh, and one more thing" things.
If it's the latter I'd be very careful. To some degree you're enjoying and taking pride in what you're doing, but getting paid for it brings in some extra burdens - dealing with expectations, obligations and financial haggling; you probably don't want to get in a situation where you need to nag a friend, or someone who's friendly, for money owed, or to withhold features from a live game for that reason.
Personally I think charging $20 for an uncoded sphere is insanely cheap. Even the $$ per hour price is really low, but at least consider protecting yourself with an estimate of how long it would take beforehand. We all know how time can get away from you while you're coding.
I hope this didn't sound discouraging.