Although car rentals in Las Vegas are inexpensive, you should think carefully before finalizing the deal. Your interest in this city will be concentrated within a few blocks, which you can navigate on foot or by bus. A rental car in Las Vegas costs about 25 USD per day, and whether you will use the car is the question.
In particular, consider that it's hard to stay away from drinking alcohol in this city, and a cheap car rental in Las Vegas may be too expensive from a safety standpoint.