If there are only two of you, the best bet is a local bus at only $2 each.
If you are only there for a week I am not sure there will be much benefit from a car.
Xel Ha is the next bus stop down the road so 5 minute journey and a long time wandering. Tulum ruins are a little bit further down the road. Many do the ruins in the morning and then go to Xel Ha so even if you do the transport costs are only $8 all in for both of you. Taxis appear to be $10 so you could share with someone!
Xcarat is another day trip. This includes the coach so that's another day without needing the car.
All that way and missing Chichen Itza? From what we could tell it could be a bit of a nightmare finding your way there and back and if you use a coach on an organised day trip the car would be sitting at the hotel again!
We spent quite a few days chilling out at the hotels, there are 3 on site as well as the Hacienda shopping area.
Many people took the $2 bus to nearby towns.
We were lucky on the transfers as we did not use a major UK company so the numbers were low. They used Taxis or 12 seater minibus. For the GBP, I would assume that there would be one direct coach regardless and it would drop off at the 3 hotels on site.

Hi
thanks for the reply, you have made our minds up and saved probably 300 pounds so thank you.
Wondered if you could tell us what the xel ha is please? we already planned on going to tulum ruins so maybe another day or 2 out would be plenty for the week and we can chill for the rest at the hotel
Many thanks again

http://www.xel-ha.com/

We visit the Riviera Maya each year and I always thought a hire car would be great as the road system is good but talking to the Thomas Cook rep a few years ago, he advised against it. Tourists (and tour operators reps!) are regularly stopped and given roadside fines for no apparent reason. Taxis are quite reasonable but we have always used the collectivo minibuses - similar to Dolmus' in Turkey - which run regularly along the main Cancun to Tulum highway and you just flag them down from outside your hotel. They are modern and air-conditioned and very cheap!

I would recommend saving the money you would spend on car hire and enjoy a great day at Xel-Ha as recommended or Xcaret, which is similar. The UK tour operators offer a day tour combining Tulum ruins in the morning followed by Xel-Ha which was excellent value.

Playa del Carmen is a nice town to visit - you can also get a catamaran cheaply from here and visit the island of Cozumel as a day trip.

Can only give a quick review of our trips.
Xcarat is a long day out with the centerpiece being a couple of underground rivers. Basically, you get a life jacket, snorkel, mask and pair of flippers and then step into the rive. there are 2 choices, One is mostly underground, the other is mostly not! We went for the light option. You swim or float down the river taking in the sights.
There is also a river boat trip and various animals on display. The Mayan Pole dancers do a couple of shows, there is an underground Mayan village and a very nice cemetary. In the evening there is an extravagant show showing the story of Mexico.
As an extra you can have a dolphin experience, not cheap but thoroughly enjoyed by the members of our party that participated. The shock comes at the end when you are given the price for photos and DVDs. $25 buys one so try and get them to take a picture of you both together!

Xel Ha is a nature area. The main activity is the river float. You get to the head of the river, put on the lifejacket, snorkel, mask and flippers and jump on a rubber ring to float down the river. there are points where you can jump into the river from about 20 ft, and my lot also found themselves swimming with a giant turtle at one point. There is a beach area or you can just mess about as much as you want. We saw a bird "flying" underwater with the fish, although strangely it didn't attempt to catch any. Thoroughly enjoyable relaxing day. They also do the same dolphin experience but are a lot quieter than Xcarat.

Both are different days out but well worth investigating.

One to watch out for at the hotels is the peso dollar exchange if you buy a service or goods. the workers work on 10:1 as the conversion ration, ie 800 pesos = $80 (hair braid), my daughter was never quoted the peso rate only the dollar cost and assumed that the figures on the bill related to that. The reception desk where you pay later does not work in dollars, they work in pesos at the hotel rate so our effort which should have cost £40 at the 2:1 rate cost £45 despite my protests.
The safe key also works out at something like 5 or 6 dollars a day so factor that into the spending money!