The Strip
Secret Pizza (Cosmopolitan, 3rd floor) - cheese slice $6, pepperoni $7. In-N-Out on Linq Lane - Double-Double $5.65. Earl of Sandwich at Planet Hollywood - hot roast beef sandwich $8. Cabo Wabo happy hour - $8 street tacos with chips. Nathan's at NY-NY food court - Coney Island dog and fries $9. All open past midnight.
Fremont Street and downtown
Golden Gate Deli - historic shrimp cocktail $2.99 with Emperor's Club sign-up, $4.99 otherwise. Heart Attack Grill - single bypass burger $8. Pizza Rock - single slice $6 (the size is enormous). The Coffee Cup (Boulder City, 20 minutes east) - basic breakfast $9. Doña Maria Tamales on Charleston - three tamales with beans and rice, $9.
Chinatown and beyond
Monta Ramen on Spring Mountain - tonkotsu bowl $12 (over budget by $2, but skip the egg and it hits $10). Kung Fu Thai (also Spring Mountain) - drunken noodles lunch special $9.50. Sam Woo BBQ - roast pork over rice $8. Tacos El Gordo (Strip and Charleston locations) - three al pastor tacos $9, some of the best in the US.
Reno: Squeeze In - the omelet split-share works out to $10, otherwise expect $15. Peg's Glorified Ham n' Eggs - basic breakfast $9.
Good to know
Can I eat cheap on the Strip?+
Yes if you use food courts, In-N-Out, Secret Pizza, and happy hours. Sit-down casino restaurants start at $25 minimum.
Are Vegas food courts good?+
Miracle Mile Shops (Planet Hollywood), Grand Bazaar Shops, and the Palazzo Waterfall Atrium have decent food courts with $10 mains.
What is the cheapest 24-hour food in Vegas?+
In-N-Out (until 1:30am, not truly 24 hours), Denny's on the Strip, and the Peppermill coffee shop which stays open around the clock.
Where is Tacos El Gordo?+
Two Vegas locations: the Strip at Casino Royale, and Charleston at Sahara. Cash preferred, no seating, worth the wait.