The one Mason that I knew ten years or so said the membership fee was around 60EUR/month. So it's hardly I-have-a-yacht-exclusive, but you still have to be able to afford it.

You may realize that a membership at a slightly-better-than-average gym is at a similar price level. Many group-based activities (i.e., tennis clubs, geek clubs, creative anachronism) have both inclusive (meet people with similar interests) and exclusive (meet less of the other people) aspects.