One of the best budget tips for Las Vegas is the fact that Hotel rates vary about as *dramatically* as you will find anywhere in the world, especially around holidays, special events, and weekends.
For example take a look at these special Bellagio rates - which themselves are far lower than the "rack rate" would be as these are internet specials for the first week of January 2011.
Second, you are absolutely right to gasp at the $90 and say "Honey, we're goin' to Vegas!". The Bellagio, along with several other premier properties like the Venetian, the Aria Resort, Vdara, the new Cosmopolitan, the Wynn, MGM, and more are slashing rates like crazy as the economy continues to hit everybody hard with less frequent trips, smaller conventions, etc. NOW is the best time in years to visit as the specials and rates are fantastic as long as you check to make sure you are going on the "off days" when the rates are low.
Note that the "second tier" hotels are also very cheap, offering beautifully appointed rooms and suites for under $50. Show ticket specials abound and food is always reasonable at many venues - though the best restaurants will easily set you back a few hundred for two so they are not for the budget traveler.
In general, as long as you stay away from the gaming tables and fine wine, your Las Vegas vacation will be a great deal.