http://cgi.ebay.com/ACARD-AEC-6280M-DUAL-ATA133-CARD-MAC-G4-G5-IDE-DISK-/200458521505

$29.95 shipped and most people have old PATA HD's laying about.

http://cgi.ebay.com/ADAPTEC-PCI-SCSI-Controller-Card-AHA-2940U2B-Apple-Mac-/270707135849

SCSI cards are even cheaper

If they have Apple ROM then they are bootable.