So, someone can earn about $2500 a month and still qualify? Food stamps are worth about $700 a month, so someone who makes $30K is getting a 25% raise off the taxpayer's dime. And that's if the only welfare they get is food stamps, but they probably get more.
I don't know about single store use for food stamps, but it should be something like WIC: You can only use it on specific items and only for the least expensive version. Also, they should incentivize saving money (i.e. you get a cash bonus of 10% of whatever benefit you DON'T use), but that probably wouldn't work.