One of the TJ providers - La Famosa - has a gorgeous two bedroom apartment with a stunning view of the city from her balcony for $550 per month, four of the Internet chicas used to share a three bedroom for $450.  As you move south rents go down.  A three bedroom duplex, for example, in Ensenada will run $450 per month.  If you are in no hurry and willing to look long and hard and speak some decent Spanish you'll find a nice studio or one bedroom for $150 - $300 depending upon location, how modern, and how secure and noise free the neighborhood.  Good luck.
Lencho