Not very much for me. I was in full time service for six years including Bethel.
Once I got out of Bethel, I figured I had already given them six of the best years of my life (ages 18-24) working as a slave/drone in their factory, so I rationalized that I had given them enough... so over the next 27 years I would say maybe $200 bucks is it.
I think their whole "voluntary contributions" idea is biting them in the ass, because over all Jehovah's Witnesses are a cheap group people with a few exceptions.
The concept is with many there is that "Jehovah will understand my situation and so let the rich brothers that Jehovah is blessing with abundance make up the difference!"
As they said in the movie Cabaret "money money money makes the world go round"