I can't tell you an exact number, but I found a more or less interesting site:

http://www.travelscience.com/framed_pages/main_frame/travel_library/Travel_Topics_DeepSea_Travel.htm

Especially the deep sea section should be what you're looking for. Especially this operator provides some deep sea tours. I couldn't find anything similar and haven't heard of it too.

When you read the description of this tour, it says that you can take some tours with a MIR submarine and it is possible that you can dive up to 6000 meters. There aren't a lot of places in the oceans that are deeper, so I can't imagine that as a tourist you will be able to find a tour that takes you any deeper.

What's the deepest underwater tour available?
I've seen this only in one scenario, 4 players on 2 teams are choosing which type of car they will use, and when both players on the same team choose the same car, player 1 says to player 2, 'Stop duping me!' or 'Don't dupe me'. The only source I can find to back up this usage is Dictionary.com, which presents no source or examples, but cites a Random House dictionary. Any thoughts?
