Actually it seems like a very reasonable price. The community (and the name) is a valuable asset. People who join Meetup discover new meetups -- it's a community with network effects. It's not that easy to reach that kind of scale. $12/month is perfectly reasonable, not because of the software, but because of the value baked into it.
LinkedIn can very easily take control of professional meetups, but no one has the brains to do it. LinkedIn has group, has events, but both features are terrible, lack good APIs and are not integrated.
I would rather join a technical group on LinkedIn with events instead of using Meetup. The community is already there and almost all of us have LinkedIn accounts.
LinkedIn: please fix groups, please fix events.
EDIT: Forgot about Google Plus and events. Another potential alternative to Meetup.
It is mostly the name that is the valuable asset. People right now think to begin their search on Meetup. Their brand is extremely valuable, but I think somebody can beat them on price and by making it easier (very inexpensive or free) to begin a new group.