There are plenty of cheap hotels in Las Vegas these days. Now you should understand that cheap is a relative term in Las Vegas. What is expensive on a weekend or during a busy convention is cheap on a Wednesday when nothing is going on. Also, Downtown Las Vegas hotels are always cheap compared to Las Vegas hotels on the strip. Prices at these hotels usually start at $50 but tend to stay low on the upper end when moderate hotels raise prices considerably.
Please do not think for one minute that cheap would imply stinky, dirty, crusty carpet hole in the wall. The Flamingo is a fine property right in the center of the Las Vegas strip. On a relative scale it is less expensive than the big resorts but more expensive than most of the "cheap" hotels. The pool area is very nice and the food choices are exactly what you need if you are frugal.
Circus Circus Hotel and Casino always has very reasonably priced rooms. You will have to deal with the kids that are crawling around the entire place. It's location on the north end of the strip does hurt its cheap factor because you have to walk or take a cab to go to the nicer hotels.
Years ago Bob Stupak's Vegas World sat at the site of the Stratosphere Hotel and Casino and it was the epitome of cheap. These days the Stratosphere looks a lot nicer but it still can be had for a low price. The carpet is no longer crusty but the walk to the center of the strip is still quite a distance.