A couple of years ago Las Vegas had an explosion of burger places. Many of them are pretty high-end (think Gordon Ramsays Burgr, Burger Bar at Mandalay, Bobby's Burger Place at Aria, the one at Mirage that I can't remember, etc.). But there are still plenty of inexpensive places around town, many of them are chains (either west coast or national). Some of my favorite non-highend are

In n Out
Habit Burger
Slaters 50/50 (lots of bacon dishes)
BurgerIM

New one opening soon to take the place of Bachi Burger is Juicy Burger at Windmill/Bermuda.

If you want to see the list of places I track (all food types) you can go to
https://docs.google.com/document/d/1IdvAu-59U_1y1ZyzODz-K5haBTfp4fv8fS4aHKhAH3g/edit?usp=sharing