I need help sorting out some problems in the fuel system. Please keep bad comments to yourself, advice and help is greatly appreciated, since im a college student and dont have lotta money to deal with fix and and fix that. Thanks.

Cant take it to dealer because i dont know how much it would cost (95K Miles)

Occassionally when im driving, the gas meter sometimes just drop lower than it was before, meaning like when i first start my car in the morning to go to class (15miles trip) based on a full tank, then when i get back in my car then start it up again, the meter drops to like half tank, also sometimes, it would sits on E then jump back up again. What could cause this problem and if possible how to fix it DIY. Thank you for your time.