Hello Czar, and welcome to CRT.
Have you tried the "Search" function on this forum? You can search apartments, and you'll get several articles about the subject.
Here's a short list to get you started:
Rincon de San Jose Apartment. This single apartment is attached to a hotel which is not prostitution-friendly, but they don't care if you bring a chica into the apartment.
Apartamentos Sudamer: I've stayed here. Very decent, inexpensive and secure building 7 blocks S. of the Hotel Presidente and right around the corner from nightclub (strip club) Pantera Rosa.
Vista Linda Apartments: Very hobby-friendly, located a short bus ride/taxi ride from all the action.
Casa Conde' - Aparthotel.
Do a search on any of the above places. If I can give you more information about the Sudamer, please PM me. I'll give you the owner's e-mail, and you can contact him directly.
Buena suerte (Good luck).