@mikeba thought i'd start a new topic for this so anyone can contribute.
Indiegogo is the one i know most about, and the flexible goal policy is really good. A lot of people choose kickstarter because it has it's own community of users who actively search for investments to make - but concepts that are geo specific (e.g. an event) aren't as well suited to this as opposed to investing in a product that can be shipped around the world.
Besides i imagine your main source of interest will come from your existing members?
This post mentions some event specific platforms do exist but doesn't give specific names