yeah--it's controlled by airport/gov. Private transfers range from $80 to $120 RT anywhere near Playa.
USA Transfers was the best deal avail. (usually our place incldues transfers but they changed it) We were between Puerto Morelos and Playa del Carmen (40 mins) for $80+ $10 tip RT. private van--changed our plans each way and email contact in mins to update. great service. we did the AI at Hacienda Tres Rios. Not cheap but good liquor and good wines, Super food.
USA even has a $30upcharge for an hour of shopping at Walmart if you do condo route!!
There is an AI just south of HTR called H10 resort and it's usually very reasonable. We went once and liked it--been remodled since our first stay--loooks good from beach walk.