Don't do it, if so, you'd need to go buy last minute supplies such as a tank, filter, heater, gravel, and all that, which truth be told is a good bit of money... And then you'd probably want to cycle the tank, which would take even more time and resources. You've got quite a few bettas, and too many more would mean you'd have to split even more time away from your other bettas. I mean, between upcoming school, a social life, and another betta, I doubt your other bettas' would get much time with you :P. Plus, you'd be breaking your vow to yourself, which never is good.
(geeze, that was really hard to type. T_T I can't tell you how much I'd like to scream "Go get 'im!" )