Every time I am at Mandalay Bay for a convention I ended up here for lunch. It isn't cheap, but it is consistent. The burgers are always good, not amazing, but the sides are really good. The fries, rings and fried pickles are always tasty.
You can build you own burger basically, so the bill can added up if you do not watch. For a burger, fries and a soda it is usually around $20, so be prepared when you sit down.
Considering that everyone else in town for a convention eats at Border Grill or Red, White and Blue it is worth the walk to Burger Bar because you can sit down right away usually.