You might want to look into Casa Andrea, a small, ten unit place just a block and a half up Francisca Rodriguez from the San Marino. Free coffee and pastries, etc. on the the patio in the morning, small pool and hot tub. Runs $450 plus the 17% IVA (tax) per week, about $75 US per night, for a small apartment with balcony with table and seating, kitchenette, great beds. She also has a couple of two bedroom units for a little more.
Photos and info at www.CASA_ANDREA.com.