I have looked and found them ranging from $13 to $50. Where are you getting yours?
From my checking different sites, I have found that sheep casings come in different grades/ratings. "E" is for emulsified like hot dogs and "C" is for a course grind, like we are making here.
I've also seen a cheap home pack ($13) that contains 142 pieces

So I settled on a place that I have never ordered from before. It's called Spice Line
1 hank of 22-24 "C" Tubed Sheep Casing for $28.95 (ouch)
What do you think?