You have several different cosmetic surgery options.
Fat transfer would cost about $1000 to $5000 (USD) per procedure, depending on where you have the work done. Fat grafting is used to fill in cheekbones, as you are looking to do. Make sure you talk to several cosmetic surgeons and get one who is experienced in fat injections, as you want them to look symmetrical.
Of the dermal fillers, Sculptra or NewFill can fill in hollows. Cost is from $900-$1600 per syringe, and of course how much you need depends on how much change you're looking for. Radiesse is another injectable filler. The results last a year or longer.
Augmentation with implants is another option. The cost will be higher, but the results will be permanent.
There's more information, with pages for all these procedures, at this site:
Cosmetic Surgery and Procedures The site also has info on what to look for in a plastic surgeon, questions to ask, etc