Las Vegas may be sin city, but it doesn't have to rob your wallet. Anyone can visit Las Vegas on a tight budget and still find plenty of fun things to do.
The mere fact that you're reading this article makes you unlike 99% of the people who visit Las Vegas. Unlike them, you've decided to go, have fun, and not gamble away your life's savings.
First thing's first, you'll need a place to stay. Scout out websites like Travelocity and Expedia for deals on hotels in the city. You may be able to find a room "off the strip" for much cheaper. If you're looking to really save money, though, you should consider staying at a hostel. If you're prepared for bunk beds and shared bathrooms, this is a great way to save a buck.
Movies may have led you to believe that the only way to travel around Las Vegas is with your head sticking out of the sunroof of a limousine, champagne in each hand. Well, maybe you're looking for a slightly cheaper alternative. Check out the Deuce Doubledecker bus for a cheap and easy way to get around the city. A 3 day pass will run you $15 and cost a lot less than taking Taxis everywhere.
Eating in Las Vegas doesn't mean starving yourself. In fact, it means the exact opposite. Las Vegas is famous for world-class buffets, and it's these types of deals you should be looking for. The buffets don't have time limits, so get there in time for brunch. Kill a few hours there with your friends and wait until you are all hungry again, then go for round 2! The brunches in Vegas should run you under $20 and actually contain some high quality foods. Ask someone working at your hostel or hotel for a recommendation.
For most, it wouldn't be Vegas if it were a sober event. You don't have to be the exception. All of the larger casinos want to encourage you to drink, because drunk people gamble more. Stake out some of the cheap Penny Slots, and start playing (slowly). When a cocktail waitress walks by, politely get her attention and order a drink. Drinks will be on the house since you're gambling, so give her a generous tip. For a couple of bucks at the slot machine, you could drink all night if you wanted to.
In most areas of the strip, you can bring your drink outside (just check with the security guard to be sure). For some free entertainment, walk around with beverages outside with your friends and take in the sights.