Here is a rundown -
http://www.artparenting.com/compensation.html
Keep in mind that your insurance will not cover any of the procedures for the gestation surrogate and that does add up.
Once the gestation surrogate (GS) is pregnant, her insurance should take over for her medical expenses.
Let me warn you right now that the process takes longer than you are thinking. We are working with our second GS (the first one did not respond well to the medicine and we had once cancelled cycle and two failures). Figure 3-6 months to preliminarily match with the GS, then there is the psych and physical testing for her (we lost a potential GS at this stage) the meeting with a social worker for you, your partner, the GS and her partner, and obtaining final approval from the clinic that they will work with her. Then there is the preparation of the contracts, you meet with your lawyer, she meets with her lawyer, and then the contracts are signed. Then you start the process with the clinic, which usually begins with a mock cycle for the GS. Once that is done, you have to get your cycles in sync for the big day. It is not a sprint, but a marathon.
Good Luck!