I've found 2 sites online selling cases -- one's at just under $5, one's at about $9, so yeah if you're supplying the UGC as well, I'd say $5 shipped is very fair.
That being said, OP if you have a local print shop, I'd look into them -- the case of 100 UGCs is about $85ish to your door in the US and the place I get my stuff printed from is about 75ish cents a piece for legal sized full color prints (I forget exactly how much, it's been a while)... So that's under $2 a pop to do it myself. BUT that involves some upfront investment on buying a case of UGCs.