At $15, you certainly have some budget to restore these guys. And they are certainly worth restoring - the D9 remain a favourite with almost all CV fans.
First thing I would do is assess the other six drivers to see if they are all working, and see if the dials for the mid and tweets are working. If you remove and unhook the woofers (put some electric tape on the leads so they don't short) you can hook up the speakers to a source to check them out. I usually keep an old BPC receiver around for this sort of thing.
Secondly, I'd put the woofers each on a multimeter to see if the coils are shot. Looking at their condition, I'd guess "yes" but I've been surprised before.
If the coils are shot, we're in a replace situation. This is best achieved by finding another used set of CVs with donor 15s locally, or hunting down a set online. To get the best value, you may need to buy a set that needs reforming.
If they're not shot, reconing and reforming is an option, based on your comfort with the skill needed. Or you could do a replace anyways.
Looks like a fun project for a fun set of speakers.