Have been watching this thread with great interest but the comments only echo my earlier thoughts on the dust masks that are around, that are also on sale at a reasonable price.
My thoughts are that the only way to go is to have a light weight mask, with the motor and batteries on a belt pack. There are some around, but are very expensive.
Although I find that the way everyone is chasing a dust mask feels a little like a case of tunnel vision. I realise there are some who are badly effected by wood dust, but is not the best initial idea to get the dust out of the work area. Otherwise it is going to be a permanently contaminated area, to which you eventually won't have access without a mask.
Until I find a powered mask that is really comfortable I am continuing along my route of removing the dust out of the work area. i.e ambient dust collectors, extractor fans to the outside, and so on. I do still wear a small dust mask when working, and touch wood to date I have had no problems. My latest project, when I can find the time,
is to try and construct a cyclone dust collector using the fan motor of my large chip extractor, and fitted with a very efficient filter system.