If you do a search on "Las Vegas" here, you'll find plenty of posts on this subject. If you haven't seen it, "our" Jonathan Gold wrote a terrific column for Gourmet about the high-end opportunities, focusing on hotel restaurants. Based on the article, I think he'd strongly disagree with you about the opportunities for great dining in LV hotels.
I've never found great ultra-cheap food in LV. My favorite hangouts away from hotels include:
1. Lindo Michoacan, east of the strip, especially for the birria and fresh corn tortillas. Generally, regional specialties are better than combination plate type fare. Full dinner will run $10-$20. Lindo has a smaller place downtown that focuses more on drinks and snack food. I strongly urge the Eastern location.
2. Mayflower Cuisinier, the first "fusion" restaurant in LV -- Chinese with some French touches, located in a shopping mall on Sahara west of the strip. If they have it, get the whole catfish -- used to be on the menu but now it isn't always available. Quiet and civilized with lovely service -- no rushing here -- a perfect place for a business lunch. Full dinner $20-$30 depending upon whether you order a big-ticket entree.
3. Right next to MF is Habib's, perhaps the only Persian restaurant in LV. Nothing spectacular, but friendly and caring and decent.
4. Maybe the food isn't extraordinary, but I'm inordinately fond of the Peppermill Coffee Shop between the Riviera and Silver City right on the northern end of the strip. Monstrously large fruit and Cobb salads and desserts (I have never seen anyone finish the fruit salad, and I know some trencherman who've tried). Cocktail service 24 hours a day and a bar that MUST be seen: Johnny Mathis and Austin Powers would feel at home there. Huge booths that you can sink into. I've seen everyone from big celebrities to professional wrestlers to families enjoying meals there. It is very expensive compared to casino coffee shop prices, so it is rarely too crowded. Even so, it's hard to spend more than $20 or so, unless you order a steak. For some reason, the burgers aren't particularly great here. Breakfast served 24 hours a day. (By the way, the food at the Reno Peppermill is even better)
5. I found a good (not great) doughnut place on East Sahara, after recoiling from a bite of a Krispy Kreme, about two miles east of the strip, but I can't remember anything else about it.