Comment by googletazer

Ads for affiliate products corresponding to the event could work, e.g. high quality (cannot stress this enough!) products from Amazon. Say, for paintball meetups it would be accessories/clothing/etc... This creates a win-win-win situation - the visitor gets a recommendation for a high quality product that is relevant and they may be interested in, you get a 4 or 8% from each sale, and the amazon seller gets to make a sale.