With control lines, as with a lot of other things, modelers buy whatever falls off the truck from other industries. As near as I can tell, that "other industry" for us is fishing line, although there may be some industrial use for itty bitty stainless cable. As such, if that industry goes to some other technology, or moves offshore, then we're left hanging (this is basically what happened with nitromethane -- it's used in a lot of industrial processes that aren't done here anymore).
So I checked a couple of fishing sites -- prices on 7-strand stainless steel leader wire doesn't seem to have gone up
too much. At least -- not enough to justify Sullivan's price increase. They've probably identified that as a slow item, and are raising prices to discourage sales -- or something.
Talk to Melvin Shute, MBS model supply. You can get yourself 1000' of the line size of your choice plus crimp sleeves (if you want 'em), eyelets, and probably a crimp tool, for not much more than that one set of lines from Sulivan.
I find it much more convenient to just make up a set of lines off of a big real than to use a line set.
Sig, BTW, sells
their version of that same line set for $25.