Beta will only work with beta system, you could damage a final system. Your market is someone who owns a beta kit but has no orca card. Probably 5-10 people in the world. And then they need an NPDP cart as well. It's hard to price. It's entirely about how much someone needs it, and that window sort of closed a long time ago. You're about ten years too late selling it. I'd say $90-125. They are rare as can be, but I think we are well beyond the time where anyone would want to try and use a 3/4 speed beta kit to play around with gamecube. Most were upgraded and the beta boards thrown away. Your best bet it to try and trade it for something you're interested in. There's no real external difference between the beta and final kits to make it more valuable either.
It's the control card for the NPDP-GDEV optical drive emulator. Unless you happen to get one that's had the target card installed, it won't work with a GBOX. If you have a GDEV and the right cable, then you can use it to run .GCM files from the disc of your PC. If you want to get it working, there are a few things you need to watch for: 1) Make sure you have the target card - as mentioned, the GDEV was shipped with them and the GBOX wasn't, but they were sometimes moved. It's normally in the last expansion slot (nearest the power socket) and looks like a wide SCSI connector. 2) Use the correct cable - it should be marked "ODEM" - it looks like a SCSI cable (and has the same connectors) but they won't work. 3) Although the connector looks like SCSI, it isn't - don't connect SCSI devices to it. One specific thing to avoid is plugging in the SCSI cable for the DDH - the later GDEVs had a (bright yellow!) warning label on the rear panel specifically telling you to avoid this. And, incidentally, you can't write the NPDP carts using either a GDEV or a GBOX - you have to use either the NPDP-GW or the NPDP-SW. Both the GBOX and the GDEV are capable of reading the carts, though.
Great, thank you for the information! And it's too light for a good paperweight. Back on the shelf it goes.