Aftermarket refoam kit for a pair of JBL 2235 (another common 15 inch woofer) is $30 from Rick Cobb - a reputable known vendor.
I have to wonder what you are getting if the whole aftermarket cone is $100 ... I'm guessing that is each ...
Is that the parts cost for the $140 recone job you mentioned earlier? Which would be $280/pr for aftermarket refurbs.
Plus shipping - and hoping they pack them well.
That's getting near real money ...