Firstly, welcome aboard :lmao:
Secondly, you have come on an corolla based car forum asking should you keep a corolla or sell it, I'm sure you know what we will tell you :D haha
Well, what your safest shot would be is get qutoes for the rust repair and just a "quick once over" with the paint and just see if you can afford it. If the car is mechanical fine and the rust is all the drama is , and the rust isn't that extensive, then I'd suggest keeping it.
IF the rust is rather bad and require fabricating and all that jazz, I'd say sell the car, because it will become too costy for it's worth.
My 2 cents worth.