I just returned from a trip in Mexico. I also looked very hard at properties as an investment. I met with some people and looked at a couple of villas. I was with another group who are now involved in buying one of the villas I looked at. I honeslty expected the prices to be much higher. The villa we were staying at was.
http://www.vrbo.com/2703
It sold earlier in the year for just over 800,000 us. It is booked solid and rents at 7000 - 8000 now per week. I looked at a smaller unit in the same community and I would advise making sure it highly desirable to renters.(meaning each room has it's own bathroom etc). One key if your looking at larger places is to make sure you employ a good house keeper. They run about 800 us a month to employ. It helps to protect the house or condo from people moving in and taking over. (thats a real law). I also employ a staff member from mexico whos parents are in realistate in cancun.
Make sure your property is close to the airport and has beach access. I found the condos to be way over priced compared to a villa.
If you have any questions let me know.