Might be something that's starting soon at the Ren, or just started. As carpboy823 mentions, the Ren on the Marriott website shows:
On-site parking, fee: 35 USD daily
Valet parking, fee: 45 USD daily
Oversized vehicles more than 6 feet 8 inches high or 8 feet wide will be subject to a USD 40 per space per day charge
What's interesting is how much the Ren is charging for parking. The Cosmopolitan, Autograph Collection, only charges 10 self-park, 18 valet park.