Best meal I had in my life was in Chinatown (take a cab) at Raku Grill. (
http://www.raku-grill.com/) Have their Omakase - you'll have no idea what you'll get but it will be fresh, perfectly prepared, and wonderful. Granted, if either of you two are a "meat and potatoes only" kind of person, you may not like it. If the idea of eating pork cheeks gets you gastronomically hot and bothered (it does it to me) then you can't miss it. Also, not the cheapest but a helluva lot less than Prime.
For a less expensive but amazing Thai meal, check out Lotus of Siam. Probably my favorite Vegas restaurant. Again, it's off strip so you will need a cab ride. But, if you don't drink, the two of you can walk out with full stomachs for under $40 total. We go there on every trip to Vegas.
Holstein's in The Cosmo has amazing but overpriced burgers. Worth doing one, though.
If you have a car, go to Hush Puppy (
http://www.thehushpuppy.com/) - nowhere near the strip but the all you can eat catfish is really good and it's really inexpensive.
Finally, if you want an excellent steak dinner that's worth the price (although it's not cheap), Hugo's Cellar in the Four Queens is fantastic. I ordered a martini and it was brought to the table in a silver shaker and, instead of pouring it all into a huge glass that loses its chill and lets the drink get too warm, they bring a proper sized martini glass, fill that, and leave the rest in the shaker, which is placed in an ice bucket.
As you can tell, lots and lots of options for steak - so if you're willing to let an experienced Japanese chef choose what you're eating, I would go to Raku Grill before anywhere else.
