I found this "store" on ebay just now. Several SCSI adapters for 2.5 inch hard disk drives. What brought me there though was the SCSI to SATA adapter! How awesome would it be to have an SSD in your old PPC mac. The downside is that these adapters are expensive, but it will keep that old mac going even longer. follow the link...
I too have been tempted by these adapters, though they are cost prohibitive. Someone should create a Kickstarter project to fabricate a cheaper board.
Those things are crazy expensive, but one day I want to get one! Thanks for sharing.
Now, I just bought a SCSI PCI card for a PowerMac G4 on ebay for $15. I imagine they'd cost around the same to produce as one of these adapters, so the high prices must be a matter of charging a lot of a niche product.