The price of a therapy session can vary. Without insurance, mine would be $110/session I think.
I know there are therapists who work on a sliding scale basis.
As for how many sessions, and how often? Depends on your situation.
Starting with reading and interacting with this forum is a great idea. You could also see if there's a support or social trans* group local to you.
I also suggest you take occasional breaks from thinking about this all the time (if needed). It can easily get overwhelming.