I help lot of people with new homes, and in my experience, unless you are an experienced builder with deep connections in the local trades (tile, electricians, flooring, carpentry, plumbing, roofing, etc), or have built several homes before, it is unlikely you will be able to build a house for less than $200 a square foot.
The cost of land in Austin is going up. Lots are hard to find, and often in subdivisions with HOAs, and required builders. Materials are expensive. And so many of the local builders have such a monopoly on the market.
Plus, unless you are going to live in the house forever, it probably won't suit the style of the typical Austin home-buyer, who is looking for large kitchens, open family rooms, nice outdoor patios, and bathrooms with large closets and soaking tubs.
In my experience, if you were to spend $200,000 in building a new house, there are better ways to invest. Take $50K, and use that as a 20% down on 4 rental properties. Properly selected, you could have great cash flow, and watch your investment increase as the housing prices in Austin continue to rise.