I don't know Raleigh well. If the hills you describe are only 1 or 2% grades, you could survive with even a 3-speed Schwinn from the 60's or 70's, which are available on Craigslist for under $100 (add $50 for new tires, chain, tubes, brake cables and brake pads). But you might be better off with an uglier (IMHO) but practical mountain bike from the 1990's, available for $100 on Craigslits.. Definitely add fenders if you plan to ride in the rain or on any sort of wet roads, and change the knobby tires to smoother ones with puncture protection as soon as you can. I would also recommend a rear rack and Wald folding baskets, available for about $20 each, and a couple good LED lights for about $20 total. That will get in under $250, even if you need to buy a cheap helmet and U-lock at Wal-Mart or Target.

You will need to look for a 17" or under MTB frame; try it out before you buy and make sure you can get the seat down low enough for your (short) legs and still feel comfortable reaching the handlebars.

Good options of your local Craigslist right now, if they fit:
http://raleigh.craigslist.org/bik/1849389990.html
http://raleigh.craigslist.org/bik/1849366617.html

Good luck!