Absolutely hiring a writer or writing yourself would help shoot your site higher in the google engines. You can write all sorts of related articles and link to your site. There are tons of content sites out there ready for rich content for college students.
Getting involved in college forums would be another excellent way to spread the word.
I think it would be pretty easy to get your site out there on the net. Also consider approaching colleges with special offers for students. I haven't looked at your business model but you could also hook up with a shopping site to offer a tiny rebate to customers and this would give you tons of advertising.
Lots of things you could do and on a shoestring budget.
BTW I just looked again at the site and think you may want to expand your model so its not just students at the same school selling to each other..that seems limited but then maybe its all you need.