I was in the Yucatan early this year and definitely preferred the vibe in Tulum to Cancun or Playa. It used to be cheaper than those places but as I understand it, it no longer is if you're staying on the beach. Tulum beach is full of trendy boutique resorts rather than the massive all-inclusives you get in Cancun and Playa. As a result, it's much more chic, with a younger clientele than Cancun but not really fratty (yet). It's sort of become a Yucatan version of Williamsburg with yoga retreats, vegan restaurants, etc. We stayed in Tulum town, which is about a 30 minute bike ride away but is much cheaper than the beach, and with more of a local vibe and a ton of good, cheap restaurants.
The weather will be very, very hot and humid in July (at least it was in January!), so that 30 minute bike ride each way will not be very pleasant. If you're really looking to chill out in the sun, I'd try to find a deal at one of the lower end places on the beach rather than in town.