I once had an experience of such a meeting.
I joined this forum in August 2009. When I went on my yearly vacation to Chennai,in January, 2010, I had the opportunity to participate in one such informal meeting.
This proposed meeting was highlighted in this forum and I responded to it with information that can help the team to be in touch with me upon arrival and make me participate.
This informal meeting was held at evening 5 pm on the day of Pongal festival, in the residence of one of the senior members. Couple of us gathered in his house and had very interesting interactions. We all then left for nearby temple, got back his home and were been offered with dinner. All at no cost!!!!
-----------
It can be planned such a way that, a member can come forward as an organiser and the gathering can be planned in the house of any of the interested participants, as suitable to all. Some snacks can be ordered from the hotel as feasible and the expense can be shared among all the participants. Participants should be interested to commute on their own, to the gathering premise.
I think, this would be the best and cheapest way to organize such a gathering. It will certainly bring members close to each other and some good initiatives for some kind of social cause may develop. People in touch can help each other for any needed assistance and information sharing that may include matrimony, government related work, spirituality, references for good job etc..etc..