Really interesting. I’m organizer of Big Data Belgium and we are fully volunteer driven. Our 7 weekly meetups are completely organised via http://meetup.com/bigdatabe as well for content of presentations as for company volunteering to provide the venue. We have zero budget.
OpenCollective could be really useful to collect some contributions and use e.g. for paying drinks etc.
It might turn out that the humonguous amount of meetup groups and probably also hacker spaces are good targets to become OpenCollectives!