I get by pretty well on around 18k a year. My friends who are TAs make it work at 14k a year, although finances are tight. If you're not absolutely set on living alone I would highly recommend sharing a house in Hyde Park or the east side with roommates. A lot of the cheaper studios/1 bedroom apartments are in crummy drab buildings far from the city center, whereas for $400-500 a month you can live in a really nice big house a few blocks from campus.
Also, don't listen to people who say the east side is "the ghetto." After living here for a year and a half I've come to conclude that such attitudes are just snobbery, pure and simple, perhaps with a little sprinkling of racism. The bad part of the east side is literally a two block stretch of one street. The rest is fine. Most of my favorite spots in Austin are on the east side.
Also, good luck! Austin is a great place to live.