have you taken a look at the cost of living index for your area? if you don't make that much or make just around it, then you can talk about the things that make the cost of living go up, like taxes and inflation. look at those numbers and talk about how they have affected the cost of living and so you would like a raise in order to be able to pay your bills.
some sites to look at:
http://www.coli.org/
http://www.ssa.gov/OACT/COLA/latestCOLA.html
http://salary.nytimes.com/