If I were set in changing C1 and only C1, it would not matter to me if the price was even $6 total, if that including shipping to me in Japan. 
Perhaps it would be more desirable to have a complete cap replacement kit offered for the original Mac 128k/512k series analog boards. And when I say "complete" I don't of course mean every single capacitor, because there are some ceramic disk and other non-fluid filled caps that would never need to be replaced. I am a talking about a kit that would replace all the caps that have the potential to leak or otherwise lose capacity after 20+ years.
Replacing C1 fixes one of the major problems with the earliest analog boards, but replacing only that cap won't solve other problems created by other caps that are either weak or dead or leaking. I must admit that I've not yet seen the same amount of "leaking" from the big caps on the analog boards of early Macs, relative to the massive leaking I see on the silver SMD caps on an SE/30 motherboard. But that doesn't mean all the electrolytic caps on the early analog boards are still working at near maximum capacity. It would be safe to say that if you use your Mac 128k or 512k and notice any kind of screen "glitches" while the floppy drive is in use, it is most likely due to one or more caps on the analog board not doing their job as good as they once did.
Something to consider seriously.
Perhaps it would be more desirable to have a complete cap replacement kit offered for the original Mac 128k/512k series analog boards. And when I say "complete" I don't of course mean every single capacitor, because there are some ceramic disk and other non-fluid filled caps that would never need to be replaced. I am a talking about a kit that would replace all the caps that have the potential to leak or otherwise lose capacity after 20+ years.
Replacing C1 fixes one of the major problems with the earliest analog boards, but replacing only that cap won't solve other problems created by other caps that are either weak or dead or leaking. I must admit that I've not yet seen the same amount of "leaking" from the big caps on the analog boards of early Macs, relative to the massive leaking I see on the silver SMD caps on an SE/30 motherboard. But that doesn't mean all the electrolytic caps on the early analog boards are still working at near maximum capacity. It would be safe to say that if you use your Mac 128k or 512k and notice any kind of screen "glitches" while the floppy drive is in use, it is most likely due to one or more caps on the analog board not doing their job as good as they once did.
Something to consider seriously.