Having visited this one a few times, now I see why Roberto's are so common around Vegas. Good food, good prices, 24 hours.
Range of good burritos at a good size for 4 bucks or less - beef, chicken, machaca and chorizo w/ eggs. With the chorizo, spring for guac and pico on it, it's exceptional. I find the chicken is better than the beef if you want to go cheap as possible IMO. Stuff like carne asada, al pastor, etc. is $5.60.
The $1 Wednesday chicken tacos are very comparable to El Pollo Loco's crispy taco and a good deal at that price. Limit 6 per person though.
Carne asada fries for $7 are bomb for the ultimate cheat day meal. Just a massive pile of Not Healthy but oh man does that hit the spot once in a while.