Temporary or Service apartments in Coyoacan? (Mexico City)

Hi there, I'm moving to Mexico City in July. I have an apartment lined up in Polanco for the three years of my contract, but before I begin work I have five months language training at UNAM and am looking for a temporary or serviced apartment in Coyoacan or San Angel. Budget is around US$ Protected content month. There doesn't seem to be much on the market - does anyone have any tips?

Thanks :-)