Magnatune (US label ) have been doing something similar for years.

Not "major" artists I hasten to add, so they have a minimum you can pay.
The minimum is low ($5 an album last time I looked). I think this minimum idea might be ESSENTIAL for folk artists as perhaps their lack of major recognition might get too many customers paying a tiny price....   then again perhaps those customers would never have bought anything anyway so its all additional sales.

I am thinking about giving the idea a go but then again I don't have a lot to lose as a part time musician.