You have misread his comment. Look at the last bit:
> What kind of crazy value would you expect something to have in order to be worth $20/mo?
The implication of that is that of tootnhcare cost more than $20 a month he wouldn't do it. Which is crazy, the expected return from brushing your teeth is well above $20 a month.
I think you have misread my comment. A regular toothbrush + toothpaste costs pennies a day, add floss and mouthwash and it would still not reach $20/month. If I can take care of my teeth by using all of those costing so little, what on Earth would I gain by paying more?
> What kind of crazy value would you expect something to have in order to be worth $20/mo?
The implication of that is that of tootnhcare cost more than $20 a month he wouldn't do it. Which is crazy, the expected return from brushing your teeth is well above $20 a month.