I went to Cancun myself with a group of friends last summer and although the nightlife was great the mongering was definitely not.
I did find one place though, Pleasure Principal, in the hotel district near the Riu Palace. Paid $200 for 30 minutes, massage + full service, but wasn't worth it considering I can get better service and pricing in the states.
Better off picking up tourists at Coco Bongo or Senor Frogs if you ask me.