I love bikes. I only wish I knew more about them...

So I'm a college student, and after my last cheap department store bike collapsed and died last week, I was on Craigslist and came across a Specialized Hardrock older model in ok condition, 13" frame for only $30. I'm only 5'-5'1" tall with a 28" inseam, but will the 13" fit me? I was riding a smaller bike with 24" wheels before, and the seatpost was already pulled out to the maximum, and it still felt a little small. The seller thinks the wheels are 24", but she's not sure. She says the brakes will also probably need to be looked at, but as she lives quite far from me, I won't have time until this weekend to see the bike. I can do basic repair on brakes, but it will be more expensive to replace them. Also, is it relatively simple/worth it to put 26" rims on the bike if it is indeed 24"? My last 24" made me feel like a little kid.

Basically, do you guys think this is a good deal? I'll be using the bike mostly for campus riding, but I also like to go off the pavement sometimes/cut across dirt fields where we're not supposed to bike. But if it seems too small, I won't have to make the long trip over just to see the bike (I don't have a car). Also, the $30 price is very attractive... I don't have much to spend on a newer condition bike.

Thanks in advance for the input!