I would love to return to Houston. How much you spend is totally dependent on your frugality. I don't buy at retail and at Houston there is rarely anything on sale. But I get a good idea of what is available on the market or coming.
Meals can be as cheap as a sandwich and bottle of water in your purse or a sit down meal. Cost of tickets is on the web so you can plan that in advance.
So in your case:
Budget for ticket, meals, and gift for the terrific friend is minimum. Anything more is at your discretion. I would take advantage of this wonderful offer as the Houston show should not be missed. A big plus is that it is in one building.