you may want to try a bottle of seafoam (lol why am I suggesting this) next time you're ready to fill up.
I understand school isn't cheap, I've been paying out of pocket until this year. I don't have a job right now either and live 120 miles from home. I drive a car that gets 16mpg average.
What is probably happening is as mentioned. There's crap buildup at the bottom of your tank. Why it happens to you and not the other guy depends purely on the contaminants within the fuel at each station.
edit: might I add, however, the benefit of keeping it at least half full vs a nice several-hundred-dollar bill to replace the pump?