Hi Justin,
We have rented cars many time over the past 10 or 12 years we have vacationed on the Yucatan.
The roads now are all very good and well signed.
Here are a couple of things to remember when renting a car in Mexico
1. Always take the local insurance - it is very rare for your normal insurance company to cover you while driving in Mexico
2. Pay strict attention to the speed limits and rule of the road - you do not want to get stopped and/or have to pay "roadside" fines.
3. Pay for gas only with cash - if you use a CC to pay for gas the CC number will likely be copied and used for items that you did not purchase.
4. When driving keep only about $25 USD in your wallet - stash extra cash you may have in a camera bag or a another innocuous location - should you get stopped by the police for any reason and they ask you to pay a fine then agree but tell them you only have what is in your wallet - ie $25.00
I've never had to make use of point #4 but other have .
Overall if you intend to do a number of off campus trips a rental car is a good alternative - however if it is just going to sit in the Desire parking area for 80+ % of your visit consider renting for just those couple of days where it make sense
One rental company that is good, reliable and reasonable is Easyway Rentacar - they are located off of the airport property and therefore a bit cheaper than most of the rental companies located right in the airport.
BTW- they offer free pickup and drop off at the airport
Here is their website
http://www.easywayrentacar.com/