Another in a perhaps-monthly survey.
My search results (run on 2/28/07) are below. Here are the parameters I used: 1400+ square-foot; single-family; active MLS listing; $300,000 or less. (See here for an explanation.)
South Austin (MLS areas 6 & 7): There are three 1400+ square foot, single-family homes listed for sale for under $300,000. The largest has 1529 square feet.
North Austin (MLS areas 1B, 2 & 4): There are 18 such houses, most in the Crestview, Wooten and Highland neighborhoods. There are none in the rectangle bounded north-south by 45th and Town Lake and east-west by I-35 and MoPac.
East Austin (MLS areas 3 and 5): 48. (This total includes a dozen or so east of Springdale, near 183, which some people may not consider "central Austin.")