Check out
http://www.eaglerider.com I've never used it, but they seem to cover a lot of cities including Vegas. It does look like all bikes run $150+ a day. Its a lot, but when you think about it for the risk of having people rent motorcycles and the maintenance of the fleet it probably isn't totally unreasonable. When I was in New Orleans a few months ago they were renting mopeds for $30/hr so $150 - $200 for a day for a motorcycle doesn't seem bad to me.
I also say rent something you've never ridden before. No one rents the same car as they own when they are on vacation.