My thoughts, i didnt read all post so dont bash me if this was already mentioned! lol
-Free to supporters-because they have already paid in to the forum
-One free to BOTM winner- with the one they already get
-One small free after 15 rep points received
-One large free after 25 rep points received
-One small free after 300 post
-One large free after 1,000 post
-Anything eles set a price then newbie's and other members can either support the forum by buying the stickers or by a supporting fee (whatever they choose)
Sound like a start? I will donate to get it started as well! Also i think if we do this there needs to be a "Stickers" section some where so new members can see that we have them and with prices, who to contact etc..