Hey, Quick use!
I've never been a student at the University of Salamanca, but I have done language training courses in the city and I've shared accommodation with some students from the University as part of my stay (Although why they thought it would be a good idea to put a 14-15 year old ( as I went twice ) in the same apartment as college kids, I don't know. I'm not complaining, ha.)
Accommodation in Spain is really cheap. I mean, even compared to US standards, your typical student apartment, shared with 2-3 people, you shouldn't expect to pay more than $300, $400 max, per month. Salamanca is great because although it's a nice, historic city, it's relatively small for its importance. So you're going to be meeting a lot of people in a short period of time and you're going to be making a lot of friends.
I would avoid the University accommodation, because standards in Spain aren't all that. I mean, it'll be clean, but for the same price, or very slightly more, you can have your own apartment with friends and be free to do what you want.
Good luck in Salamanca! I had a Hell of a good time there. I still remember it like the back of my hand. You should hopefully enjoy it.