It's precisely because my own "tradition" (I don't particularly like the term) also places an emphasis on using a paper as an organiser, that I'm pretty skeptical of the various stories you hear about the SWP and their quotas and their secretly-paying-for-unsold-papers and the like.
In my experience (different party, different country), a miniscule percentage of the total sales of our paper come from "personal sales", where a member takes a few and sells them to people they know or meet, in the first place. Members are encouraged to take some, but it's really a pretty low priority. And people would thing you were nuts if you were habitually taking a bunch of papers, not selling them and then paying for them yourself.