I'd honestly could say that my college years were my most,"Maaaaaan I'm sooooo broke!" times in my life and it wasn't spent on bars and partying.
Depending on what you are majoring in you might not even have time to really work on the car if it needed work.
Although having a car to work on will definitely keep you sane through these times but you do not want to put more pressure on yourself than what you already have.
But this is your decision so just like everyone else has added in I will contribute my advice by saying,
"Do whatever makes you happy and hope that it will serve your purpose, there is no fate but what we make for ourselves." That last bit was quoted from Terminator 2
So if you want to have an SR240 or any RWD car to fool around in and get you to school even though it has rust then do it. But do take into consideration of the consequences in the decisions you make as many people have listed the scenarios above.
Personally from experience and what I would've done at your age, even though I know money is tight I would just find something that was somewhat and mostly reliable and easy to deal with if work was needed.
I bought an sr5 AE86 while in school and it had a rod knock, did I regret it? No, was it a smart decision? No, but I had fun working on it and doing a GTS swap, I still have it to this day because it still makes me happy just as it did from day 1.
Also a fixed up 240 will get you more girls than a fixed up 86, with an 86 you will just get dudes so yeeeeah, think about that