Yes, the costs are per room, rather than per person.
Rates are particularly date-specific in Las Vegas. Just to give you a benchmark, I used QuickQuote (above left) for your dates. In Hotwire, for a South Strip 4* (the area in which Mandalay Bay is), there are three choices - $93, $91, and $84. Of course one has to add in the Hotwire fees andtaxes, plus resort fees at the hotel. With a tighter budget, there also is a 3.5* at $59.
"Near by" Mandalay is subjective, but the South Strip isn't a particularly large zone, so one can't get REALLY far away from anything in it. It is a little over a mile in one direction, and less than that in the other.
I didn't look at Priceline Express, but there undoubtedly are offers there also.
If you look over the Hotwire and Priceline Express possibilities and see something you like, you can post back with the details - date, rate, area, and amenities. The experts here can give you an educated guess as to what hotel you might get.
With Priceline bidding, you have to accept anything in the zone at or above the star level you bid. At the moment there are 6 Priceline zones that don't have 4* or higher bidding. If you want to try bidding the zone you want, these are available for giving you additional bids. As a general rule, one can do a little better with bidding, but one gives up the educated guess as towhat you'll be getting (Priceline Express and Hotwire).