One tip for finding a space, try your public library! Mine has plenty of meeting rooms that can be booked for free.
I initially was buying pizzas for the meetup, but they didn't really get eaten, so now I don't bring anything but an HDMI cord.
YMMV, our public library has free meeting space, however they absolutely will not let you sign up for a room monthly.
One of the biggest issues is having a consistent meeting schedule, juggling the day/time makes it hard. You'll never find a time that works for everyone, so just pick one that works for the core participants.
I was heavily involved in running several meetings for ~20 years, and we'd regularly have 30-50 people at them.
We got space from, at various times: Businesses, Universities, NIST, Hackerspaces. Check around, it can be pretty tough to find space, especially for larger meetings and meetings that need projectors for presentations, but we always were able to find a place.
Ours seems to