ATM business isn't that bad I hear, this isn't so much a recommendation but check out if there's any demand for Bitcoin ATM's in your area, they may catch on. Knew a guy over IRC who started building a monopoly on them in his area, seemed to be working okay but I'd be concerned about keeping it secure, you don't have the benefit of Visa/Mastercard conglomerates allowing chargebacks if someone used a stolen card to cash out your ATM.
Honestly though the only guaranteed way to earn money is be employed, if you're only getting 3 hours ask your boss for more hours. Or see if you can reduce your class-hours next semester.
Pawning stuff on ebay always works great for passive income, especially if you can find some niche, rarer products. Remember to retain records so you can file taxes!
I'm also interested in what degree you're going for.. hope you didn't take any loans, college is wayyyy overpriced. Sucks to be American.
If you wanna go all-out learn to trade, it'd make trying to do any startup business a moot point if you have a powerful enough lust for money to do it right.
In any case, good luck.