Just off the top of my head I am giving you these answers. I haven't had much time to research anything seeing as I work 50 hours a week on 3rds. Usually when I mail out the winnings I do it on my own dime unless I am running low on funds that week. I checked Media Mail at the usps.com. This is something I will have to get with my local post office to see how it works.
Yes, I don't mind paying for the shipping from the post office when I have the money to do it. Sometimes I am not able to though. Just depends on the week and how work goes.