Those packs of loose partridge and grouse feathers often have barbs sized 2-12 - except for a few 10's and 12's too long for most trout fly sizes when wound around the shank.
Frank's thread is a great link for working with feathers with long barbs.
But if you're looking to get into soft hackles, you'll want to pay attention to barb length to match up with the sizes you'll be tying.
To start you might want partridge and starling skins:
Partridge skin-- will have feathers from size 14 to 2 about 25-30 bucks
Starling for small flies size 16-24 about 5-6 bucks
If you hunt or know some that do, all kinds of stuff from woodcock, pheasant, different partridge, grouse, and quail have great feathers. In addition to the "cape area" (neck) look at the feathers from the wing coverts
Capes will generally have a more useful range of sizes for soft hackles than saddles. "Genetic" hen capes raised for fly tying will generally have more useful size ranges for softhackles than imported "Indian" capes but will be more expensive. In addition to Whiting hens, the JV Hens (juvenile hens) from www.conranch.com
are exceptional for softhackles with flexible easy to wrap stems and great barb length for trout sized flies.
Looking at some of the stuff I have lying around here to give you an idea of feather sizes and prices:
|Indian Saddle ties sizes 12-2 about 4.50|
|Partridge Feathers 12-2 2.50|
|Whiting Brahma Cape 18-2 12.00|
|Whiting Brahma Saddle with Chickaboo 10-2 12.00|
|Whiting Coq de Leon Hen Cape 14-2 22.00|
|Whiting Hebert Miner Hen Saddle 12-6 9.00|
|Whiting Hen Cape Bronze 18-4 18.00|
|Conranch JV Hen (includes cape and saddle) 20-4 25.00|
|Conranch Mature Hen (includes cape and saddle) 16-2 35.00|