As long as you are on The Strip (Las Vegas Blvd, between Sahara and Russell), you'll do pretty good. Excalibur is a decent "lower cost" hotel and is in an EXCELLENT location. But, it is older, having been built in '89. Keep in mind that Las Vegas Blvd is a very long street, but only a few miles of it (as noted) is actually "The Strip", so be sure to look up addresses, if you are in doubt.
I've been hearing that Planet Hollywood has been offering some pretty good deals, so it pays to do some research. Also, while I haven't done it for Vegas (since I live here), I've had success with naming my own price on Priceline.com. You can't request a hotel, but you can "stack the deck" in your favor by selecting a certain rating and narrow down your search to a certain area (South Strip and North Strip are both options - Excalibur is South Strip). Then, you name a price and they'll let you know if it is accepted. Start low and work your way up to whatever your limit is. I ended up getting The Drake in Chicago for $99/night by telling it I wanted 4 star on Michigan Ave.
Good luck with your planning and enjoy your trip...