We always recommend renting a car while visiting the Riviera Maya. There are many little roads to travel and places to explore, most of which is best done with a rental car and comfortable shoes. Car rentals can be easily completed online at any of several websites and are often very affordable. We have found the best rates by reserving cars online, prior to arrival.
There are rental car agencies in Akumal such as Akumal Guide. The rates are usually higher when you rent locally (around $70 US per day for a Nissan Subcompact), but if you only need a car for one or two days this is a great option and the service is excellent.
Although we are not affiliated with any car rental companies, most of the major rental companies have locations here in the Riviera Maya. Hertz, Executive, Avis, Thrifty and others have offices in Playa del Carmen, and Executive has a location in Puerto Aventuras that will deliver your car to Akumal. An easy website to navigate is Easy Way Car Rental in Cancun: http://www.easywayrentacar.com/.
During low season (August, September and October) you can sometimes find a good deal by negotiating directly with the agent at the desk, but we always recommend shopping around before you go and having a good idea of what you can expect to pay.
If you have a baby or young child, you should either bring your own car seat or booster seat with you, or make sure that the rental company has one that they can rent to you. Here in Mexico it is not a legal requirement for children and babies to travel in car seats and you may find that some rental companies just don't offer them.
When shopping for car rentals the following information on insurance may help. Insurance is broken down into different categories. The required insurance is the "Additional Liability Insurance" also known as the ALI. We recommend the Collision Damage Waiver (CDW) and Theft Protection (TP) also. It is preferable that you purchase these through the rental company, they are however often available through major credit cards. Please check with your credit card company for availability and details. The trick to renting a car in Mexico is understanding the need for liability insurance. While often listed as "optional" liability insurance is a must have when driving in Mexico. Additionally many car rental companies will place a large "hold" on your credit card should you choose not to purchase their insurance. (Often in the neighborhood of $2,000 US). The cost of liability insurance is seldom included in the daily or weekly rental rate quoted online and is generally only disclosed in very fine print. It is important to have proof of insurance on hand in case of an accident or dispute. This will save you both and time and money.