The Texas information comes from the UIL 2005-2006 Basketball manual (on p. 10). Here's the pdf link:
http://www.uil.utexas.edu/athletics/...reg_season.pdf
For the chart's "example" purpose, assumed 250 paying fans for the doubleheader at $4 each for a total gate receit of $1000.
The links on the web page will take you to the online (or downloadable) documentation where the data came from.