Get a SCSI drive, they are fully compatible Mac/PC so are priced OK. If you do not have SCSI internally you will need to also get a PCI SCSI card. I've got an Adaptec Power Domain 2930 that works fine. Bought it a number a years ago so I'm not certain if it is still around.
If you want to go really cheap, you should be able to find this sort of equipment second hand. Be careful about the different types of SCSI (narrow, wide, ...) since it has to be compatible.