2003 Saturn Vue Transmission problems?

So a couple months ago I bought a 2003 Saturn Vue from a private owner and recently it has been really rough with shifting. It is an automatic but when i put it into reverse at times it won't move and sometimes when its in drive it reverses or doesn't move. Basically I always wonder if my car is going to drive when i get into it. So far turning it off and on a few times usually does the trick but i took it to get looked at and was told my transmission is bad and could give at any moment. Now it has the saturn transmission not a Honda one, and they are hard to find from what I was told and VERY expensive. I was wondering if I could contact GM or someone and get it replaced or if I could swap it out with a cheaper transmission and a better working one? Do I have any options other than getting rid of the car I just bought and love. I'm a broke college kid in the country, I need a car.