I'm afraid golden plover doesn't come cheap. Best source I know is Jim Slattery http://www.jimsflyco.com/html/wet_fly_supplies.html
who carries a good selection of other skins for traditional soft hackles.

If you are thinking of using partridge, I think you would be much better off buying a whole skin rather than a package of feathers. The package will not have the smaller feathers that you will want to use, and one skin will last you for a long, long time. It's a bigger investment up front, but a much better value for the money.