Sounds like the dog teeth got fuct on the 3-4 slider. Fourth gear is realy not a gear, it is when the input shaft and output shaft lock together and create a direct drive. Could also be that the 3/4 slider assyembly is fuct, since you can't get it into 4th with the car off. Or maybe the 3/4 shift fork is cracked. You really can't tell untill you open her up.
If it were me, and i know cause I am in college and also broke. Keep driving her until you save money up to get the tranny fixed, or you have money to replace it with another one. I will put money on it that you can drive it for a while (as long as you don't beat on it i.e. no power shifting) And it will last, since 4th gear is really not a gear. just skip the gear go from 3rd to 5th, i know it is a pain, but you gotta do what you gotta do when you are strapped for cash. It is also possible that 3rd may go out on you.
Just thinking about it, but I don't think it will help, if you pull out the shifter, you will find that the end of the shifter that sits in the tranny has a plastic ball on it. If that is fuct you won't be able to get in any gears. You can check this out and it is cheap to fix, but I doubt it is your problem.
Mario
