Zumper, Craigslist, local campus newspaper will get you an idea. Don't look at it as cost per house, student housing is a price per room gig. I get 400$/month per room whether it's a 2 bedroom duplex or a 4 bedroom house.
In my personal opinion you don't need to pay attention to what they're charging on-campus, completely different ball game. Look at what other off-campus student rentals are getting, that's the only thing that matters.
I own 15 of these, and maybe some of the markets are different, but the fact they're going to school and may or may not be there in the summer or winterim is completely irrelevant. My students sign 12 month leases, I haven't had a vacancy for any of my student housing units. One market I invest in is a June-June cycle, and another is August-August with the big "push" in renting being in the fall so I have that written into all my leases they need to inform me of their intent to renew within 9 months of lease termination or I can begin marketing their unit.
I also end leases one week before the next students come in, this gives my team enough time for turnover and can get overlooked. I also offer an as-is move-in, some students are fine cleaning it themselves if it means they can move in a week early.
