Welcome to the forums JenniDoll.
I don't have a PWS but my daughter who is 5 does. My heart goes out to you. Let me say congrats on your upcoming wedding!
Laser is the way to go to get rid of the birthmark, and as far as the money situation goes, you might be able to find help from your local city government aid. I am not 100% on that though. If you were to have surgery in one week from today the birthmark unfortunately wouldn't be lighter by your wedding. My daughters birthmark after surgery is much darker for about 2 weeks, then goes back to her original color. Within about 6 weeks I usually see a change in the color of it. I know that isn't what you wanted to hear but at least you are able to be informed. I won't pretend to understand what you are feeling or going through bc I can't. All I can say is that you have found a great support system here hon. I love these forums and I just joined last week. The group of people here is wonderful, they will answer your questions, listen to you, and give you advice.
Good luck w/your upcoming wedding.
PS congrats to you Kim on your upcoming surgery.