Hi, I'm looking for a cheap bike that I can just ride around the campus and I have picked several but don't know which one I should pick, so please help me to decide the best one out of these Thanks!!

http://seattle.craigslist.org/see/bik/2659023450.html
http://seattle.craigslist.org/skc/bik/2658744857.html
http://seattle.craigslist.org/see/bik/2639968668.html
http://seattle.craigslist.org/see/bik/2658472219.html
http://seattle.craigslist.org/see/bik/2658464942.html
http://seattle.craigslist.org/skc/bik/2658349511.html
http://seattle.craigslist.org/see/bik/2657925236.html

I just need something cheap and solid that will last until I graduate which is next JUNE!!
please help me to find a good one

Thank you