In San Andres, you can find anything from high-end resorts to family hotels, all-included packages to more rustic cabins. Most lodging is found in San Andres Town, with a few options in San Luis. More expensive than the mainland, prices really peak during high season.
As for Providencia, accommodation and food are pricey. There are fewer lodging possibilities than you find in San Andres. Most travelers stay in Aguadulce, though some opt for Santa Isabel or Bahía Suroeste.