The first rule of negotiation is to not give a shit.
If you care about the job, you risk losing it, if you don't give a shit, you will more often than not walk away with a better deal.
If you're ok with the odds, just tell them that you think the offer is very low based on your research online and after talking to career services at school, along with the fact that you thought the interviews went great and that you have student loans (all great reasons to ask for more money, come up with more). If you got the contact info of your interviewer (not HR, the real person who makes decisions) - email them expressing strong interest in the position.
But, above all, be prepared to walk away at any time, if they think they have you, then they have no incentive to give you more cash.
If this was a startup might advise would be totally different, at that point you're doing a job out of love than just for money :)