The guys at Scenic Airlines are incredibly helpful to airline staff, on production of an ID. I have taken 3 sightseeing trips with them over a period of 12 years, and each one has been cheaper than the last! If seats are free on closeout, they'll try to get you on. I once had my whole family with me (7) and there were 7 no shows, so incredibly we all got on.They leave from the smaller Las Vegas airport, (I think it's Las Vegas North?)I think my last day trip in 2005 (lunch, rtn flights, rim tour etc) was $25! I can't praise them enough - they are brilliant.
Hope this helps!