I'm likely to agree that it's not gouging for no good reason. As far as I happen to know these devices haven't been manufactured in a few years, so it's not exactly as if someone's buying parts for $3 or even $30 and then marking up the price 10 or 100x.
These devices were manufactured for a couple years back when it made more sense to buy a Firewire adapter for your Jaz drive than to buy a new Jaz drive (And, thinking about it: IIRC the Jaz drive only ever really shipped in SCSI versions) or to move to a new type of storage/transfer cartridge altogether.
Or, if you had a bunch of SCSI peripherals that cost more than storage peripherals tended to do (especially once people started to move to USB/Firewire external disks rather than cartridge systems and didn't want a multi-machine workflow (which I tend to advocate for these days, because often the machine best equipped to
acquire an image or a video isn't necessarily the best one you have to edit the content or ultimately transfer it to the Internet, but that's a much newer concern, really.
At this point, in some circumstances, it might be easier to think about just having, say, a G3 or G4 tower equipped with both SCSI and USB/FW to use with peripherals like these.
(Except the SCSI2SD, explanation below)
Bam: dual interface drive that can be read by a classic and modern Mac
Depending on how your SCSI2SD is positioned physically, you should be able to take the card out and put it in an SD card reader for use on a more modern system. I believe you can also (on the v6) mount the card over Micro USB. I wouldn't waste a scsi/fw or scsi/usb adapter on that.