I don't think I've ever run into an issue of a show being sold out. But, if you book early, and look online a lot of times you can find good deals. A lot of shows are on Goldstar, and Cirque sends out some really big discounts a few times a year.
The 1/2 price places are kind of a crapshoot, and it's never half off fyi, it's like 1/3 or 1/4 or like $10 off... If your heart is set on something check it out before.
http://www.smartervegas.com/shows/lo...discounts.aspx here's a deal 25% off LOVE. i'd guess that would be about the discount you would get if you went to the half price place.
Barrett Jackson Family Trip!