For that range of sizes you will need to buy a Neck or necks. If you want more than one color try to find a supplier who will sell you two half necks for one price. You do not need the top grade of neck but will need hackle raised for fly tying to get down to a size twenty. A suggestion for keeping the cost down is to plan on some substitution of colors. A dark ginger or light brown neck will do for both brown and ginger as called for in patterns. I have often used grizzly hackle instead of dun and it is much more versatile overall. I would start by looking at the patterns I intended to tie. Decide what hackle is needed right now and what can wait until later. If some colors will only be used in limited sizes consider saddles or half saddles. If you want to make a show of trying to be frugal buy a rooster from a local farmer and have chicken soup. The feathers will be good for streamers and wet flys. Usable dry fly hackle in the larger sizes is available from fighting cocks. Caution should be exercised in contacting those breeders. They can be violent men but they will sell a bird if approached properly.
I can think of few acts more selfish than refusing a vaccination.