Hey guys,
I had the opportunity to go to some of these in NYC. I had an amazing experience. There were a lot of SB type women. Most of them look like 'Civvies" than dancers. I really like the "Natural look"  It was like going to a table at 1ok but you get touch the chick. I even ended up getting a kiss and getting some phone numbers as well. Also most of the guys were chill, they pretty much didn't care and the dancers would approach the guy and not the other way around. They also had events outside of NYC. I've been to Las Vegas clubs but to me this is more of the experience I'm looking for.  

Where do they advertise and what's the ballpark cost?

NYC, if you ask around eventually, you'll run into them.

Are you talking about "floating clubs?" In NYC, the owners / organizers would find vacant spaces in various commercial buildings that they could rent for short periods. After a few weeks in one location they might disappear for a while and pop up someplace else.  
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They were written about in the NY Times and other newspapers from time to time.  One of the owners was interviewed in, hmmm The NY Post (maybe?), and he bragged about how he was too smart to be caught and shut down. So LE caught him and shut him down. Beware the sin of hubris.
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I had been to a few, years ago, but I no longer have the right contacts.

Yes, something along those lines. Though some are simply advertised as "private parties." As you said you can become a member and be invited.

But it anything BUT low key, chill, or casual.  The hosts ran it more like an Atlanta Hip Hop Strip club, with expensive bottle service, and many thicc dancers twerking while high rollers made it rain all over the place.  

Only 10 million people to ask in NYC! I think your post might be a shill or something. How can something with no advertising be any good. It is hard enough to find quality providers even using TER and other sites. If what you are describing is all under the radar then I struggle to see how one can be assured the quality will be good.

This is done two reasons one keep you keys from you. Two spice things up it most done with the younger crowd  21 ish. Also common callow a orgy party.  Have to know who to ask most providers are into it however it a civil thing.

A famous one in NYC was called “Hot Lap Dance Club.”