Updated June 2016:
TravelZoo has extended their discounted tickets to Penn and Teller at the Rio. The offer now good through October 22, 2016.   It seems like they renew it or add another ticket offer just like it on a regular basis. With the discount, mezzanine level seats are $46.10 plus tax and fees. The regular price is $76.84 plus tax and fees.  They put on a great show; definitely worth the discounted price. It is on my Top 5 Shows list. You can see my review here.

Here is the TravelZoo link.  The link on their site will take you to Ticketmaster with the discount applied. If  you would prefer to book over the phone you can call 888-746-7784, press 1 and mention offer code ZOO.