Please forgive the shill.
A friend is involved in the construction of
this development in Huatulco. The apartments and amenities are superb, I can attest first-hand.
Owners typically rent out their properties for short vacations (often residents of Mexico City etc coming down for long weekends etc). My understanding is that because there is still construction/sales going on (deliberately gentle build, over a number of years), apartments can be rented at good value for money.
I've stayed at the Camino Real, and thought it was pretty decent, although it can become a zoo at peak periods. The beach is excellent.