FFS is considered to be cosmetic surgery, so there are no requirements or pre-requisites to getting it done. Anyone can do it at any time. Ironically, it's actually easier to get FFS than HRT...
But because it's cosmetic surgery, health insurance will not cover it. You have to pay for the entire amount out of your own pocket. Most people who have had it will say that it cost anywhere from $20,000 to $50,000 US dollars. Different surgeons have different pricing. It's a good idea to get consultations with multiple surgeons before deciding on one.
It's also important to realize that although it doesn't require approval by a system of therapists or psychologists beforehand, FFS is still serious, major invasive surgery. You will be under general anesthesia. As such you want to be in good health and physically fit to improve your chances of a good outcome and a smooth post-op recovery. Surgeons will also require you to be medically cleared before surgery, so you will need to undergo a number of tests. These plus the cost of aftercare should be taken into account when calculating the final cost of FFS as well.