Where do get accomodation in San Juan?

I want to spend about a month in the San Juan area (really as far as I can get without a car because that would be expensive). I'm planning to go from mid-March to mid-April.

Is AirBnB the best option? Is there something better? Is it possible and realistic for me to rent for just a month? I just want the cheapest private place that isn't a scam and is safe. I would also prefer to be in the place where the least English is spoken that I can get to without a car, but that's not a necessity.