We'll be at show from the 14th to the 17th at the Sands Expo. Recommendations for inexpensive places within walking distance would be great.
Beating $15 a person is going to be a toughie, as you can imagine. I don't know if you've been to the convention center before. Basically, it's attached to the Venetian and Palazzo casinos. Your cheap food options are basically gonig to be the casual dining places at the Venetian, at the Casino Royale, at the Mirage across the strip and at the mall catty-corner from the Palazzo.
The mall and the Casino Royale will have all of your chain favorites. If you just want a Chipotle to get some decent food and quick calories, that's the way to do. The mall has a Vegas outpost of Grimaldi's Pizza, justifiably famous here in NYC. I can't say how the western version is.
There's a BLT Burger in the Mirage which was pretty good. But you won't stay under $15 if you want one of their signature spiked milkshakes.
Closest of all are the casual restaurants at the Venetian/Palazzo. Those are listed here: http://www.venetian.com/Las-Vegas-Res... Turns out they have a Grimaldi's, too. Go figure. I haven't been to any of those places except for Otto, which you won't get out of in your price range unless you split a pizza and have tap water. But I'd say just pick your favorite TV chef and try his place. :)
There is a Tacos El Gordo just North of the Wynn on the East Side of the Strip. It's about a half mile walk each way, so round trip should only take you about 15-20 minutes. I have only eaten there once, but the tacos were good. They are small, but only $2 each.