Hey! So for UT Austin, I asked them if they were reimbursing us (this was an informal conversation over the phone with someone not in my program) and he said yeah. I think it varies from school to school because UC Davis invited me to visit campus for an interview and they didn't mention anything about supporting us to go there. Then 10 minutes later I got an email from the same professor that read something along the lines of, "Because you have a good academic record, we're giving you $100 or $250 dollars to visit depending on if you're instate or not."
Are you visiting the school for an interview? If so, it may be rude to ask, but if you've been invited it never hurts -- I guess. Also if you're looking for cheap tickets studentuniverse.com sometimes has really great prices on flights.