Oh yeah!!! Totally right JP!
Some of them really get you on the insurance. A few even charge extra for glass and tires! No way should you drive around with just a credit card insurance. The way it was explained to us- "If the cars, uh, touch with damage, everybody goes to jail". God forbid one of the vehicles is a Taxi. You will be surrounded by 47 Taxistas saying, "Gringo did it". Thats why we have a dash cam in our car! Here's one!

By the time you factor in side trips on the colectivo, a few Mega or Soriano taxi runs, we always found it easier, if not close to the same price. Add the convenience factor of not having to hoof it in to Xel-Ha, Punta Venando and Xpu-ha from the highway and throw in an expedition to Coba or Chicken Pizza, Rental seems the best option for the OP.

Not all car rentals are the same.
We do know of two agencies who include insurance with the rate; America Car Rental and Caribbean Car rental. Our neighbor rents a car for around $150usd a week including insurance, someplace down by Plaza Antigua.