The donation arrangement started in the USA due to some issue with tax and charitable status. It came to Britain later, on Jan 1st 1993 (I was on Literature at the time).
At that point we were charging 15p/magazine or 25p for two. Small books were £1 and the larger books (e.g. the Blue "Creation" book) were £2. Larger items could pretty much only be picked up from the literature counter, though sometimes bibles were sold. I forget the range of prices for those, as we were only supposed to "place" the cheaper hardback ones. The "delux" leatherbacked ones were about £5.25, as I recall. Insight volumes were about £10.
One of the hoohars surrounding the change to "donations" was that the Pioneers would no longer earn a profit because of the discount they had previously enjoyed, while being expected to charge at the full rate. It was one of the few perks of the job. I never really turned a profit when I was Pioneering, as I tended to give away a fair bit of literature, as it was offset by the "earnings". It ws hardly a big deal, to be honest, though for some Pioneers with large "routes" of maybe 1000 magazines, they could be turning a profit of £90/month, which often paid the fuel costs for the car.
This was all just to cover the cost of printing, of course, but selling is exactly what we were doing.
I recall a visit to Africa, in I think 1999 or thereabouts. My [ex]wife and I were delegates at the International Convention in Nairobi and helped with the literature. We were charging people 50 Kenyan Shillings (equivalent to 50p / $1 / a day wage for many) for the paperback book that was released. Some of these people couldn't affford shoes, yet we were merrily set to the task of charging them. I understand that more recently they finally changed this arrangement.