There is much discussion on this topic. I bought my kids pins from cheappins.com for under $3 each, and they are disney copyrighted pins. The traded strictly with the cast members and had no trouble at all with the trading. The cast members really enjoyed getting some of the pins as they are different characters than are seen on the racks. Also you can try Dizpins and go to some of their links for pins for a good deal. I have also used going24-7.com but they are the regular price plus a little, although you can get some awesome traders from DL from them.
When we were there last week cast members allowed the kids to trade anything no matter what at AK, adults could only trade if they didnt have it on their lanyard already. At MK, MGM, and Epcot the kids could only trade if they didnt already have it on their lanyard. Just ask what the rules are before you trade.
Also if you are thinking of ordering pins do so quickly as they may take a week or two to arrive and you dont have alot of time left before you go.
By the way my kids used Hats for their pins, and I was glad I chose that method as the lanyards seem to bite into your neck when they get heavy.
hope this helps a little.
