You could also check out Comfort Inn. It is directly across the street from The entrance of the Joint and convention area of the Hardrock. In most cases you will be closer and faster to get to the convention than anyone staying at The Hardrock.
If you get an Efficiency Room, you will have a small kitchen included which can save you some on food or ample alcoholic beverage storage.
Looks like it will cost you $55.00 - $65.00 per night.
This is also the best option for moving for 1 night from the Hardrock and back. Done it a couple times myself.