The money that this tract of the early 20th century, priced at 1/2d, is worth today, is perhaps 6 or 7 shillings? That's some increase, but that's not where it's worth lies. If a tract costs £100 and given to an unsaved person leads to their eternal salvation, what return is that! Tracts are often available for free and may lead to salvation that is free, but taking it to the unsaved often comes with some cost.