Where are you from? It helps to know since recs can be tailored to what you normally lack access to.
I generally dislike Buffets, but the one at CP is legit. good. The one at Harrah's is about $25 and fast. The carved meats are good. (KGB Burger is indeed closed).
There are a few places to grab a slice of pizza, which is a good lunch option. 5fifty in Aria is very good, next to the poker room. About 5-6 bucks a slice. One of the tricks of vegas though, is NEVER buy sodas or stuff like that at these places. It will be like $5. Either get it from cocktails or, better yet, stop by a store on your way in from the airport. Buy a bunch of drinks, alcoholic and non. Buy some granola bars and fruit or whatever. This will save you $100.
Bally's lacks the dumpy qualities of some of the other cheap places. I would be cheap on rooms, since you don't spend much waking time there. $50 a night in rooms = dinner at some elite restaurant.
Rao's at CP is one of my favorites in terms of bang for buck. Old school italian. The chicken scarpariello is unbelievable. Dip bread in sauce, inject into veins. I believe it's $30.
Aquanox at Venetian/Pallazo is a great sea food place. It's maybe $30-$40 an entre, but better than some more expensive places in my opinion. That's where I always steer people in Venetian.
If you want an experience, Rose Rabbit Lie is just insanely hip and affected, but I found it fun. Our waitress carried her purse. They have some kind of show, but we just ate there. The food was creative and tasty. It is more expensive, but not quite to the crazy Guy Savoy type levels. I wanna say $150 a head or so.
A more conventional fine dining place is the eiffel tower restaurant. You have to wear a jacket, which is kind of fun in a place as ridiculously casual as Vegas. You get a view of the Bellagio fountain from above and it's like watching someone make giant, abstract paintings.
One of the best thai places in the U.S. according to Anthony Bordain and people like that is about a mile off the strip. It's not expensive. It's called lotus of siam. You need reservations. There's also a big asian area off the strip on Spring Mountain. If you normally don't get stuff like Vietnamese, there it is.