Austin takes a 1% fee on top of subtotal. So a minimum fare is 6-8¢ depending on TNC, while an airport run from my neck of the woods nets the city 34¢ or so.
Let's assume that rides are an average of $12, and that there are 120k rides per week across all TNCs (probably more than that, but there's plenty of seasonal variation). So over a year the city's looking at $750k in TNC fees. Fair chunk of change, but not a crazy windfall by any stretch.