There doesn't have to be a prize. Have a jig contest once a month where members send pictures of their jigs for the month. Then have a single post where all the jigs are posted in the first post in a single picture and we all vote on them. Winner jig gets show cased for the next month.

Setting rules/restrictions on materials makes it more fun.
All one color
At least 3 colors
At least 5 colors
Ugliest
Prettiest

Winner picks the restrictions for the next month and no one wins more than twice a year. Could be submit entries until the 15th, vote until the 29th or something like that.