> No salaries, no office. My two cofounders and I have
> been throwing everything we've got into this; we're
> all broke
To put it nicely, "So what?" (I know that sounds cruel but trust me it isn't) What you have is a bit of traction, you don't actually have a business yet and as such its probably too early for any but the most inexperienced of investors to invest in you.You know you need more than the three of you, but lets focus on one school for the moment.
You need a "listings manager", a "sales person", a "student rep" for a school. Lets say your "unloaded" salary pool is $100,000/year (that is salary but not benefits cost[1]). You'll need revenue from advertising at that school to exceed $100,000 annually. Since you're just proving this out you three can presumably "play the role" of the three people you would hire here to do this. So you need a minimum of $8,500 per month in advertising revenue. You should target double that or $17,000.
Once you have one campus working, where it is paying more than enough for your three "campus specific employees" then you can start to think about investment to go further. An investor is going to ask you questions about "What does it cost per campus? what can you make per campus? What are the limits on that?" you will need to have really good answers to those questions which you don't currently have.
[1] This is a 'swag' or scientific-wild-assed-guess on an number, I based in a student working part time during the year getting about $10K/year (1000 hrs @$10/hr) A sales person being paid mostly on commission ($30K/year + 10% commission for $10K out of the advertising sales, and your listings manager making $50K a year straight up) You should adjust those numbers based on your own experience/insight