Just
do a search on Google or eBay
for "SCA SCSI" (loose the quotes).
How much should I expect to pay?
Depends on where you get the drive, and how big. I typically get
used ones for free. A new one will run you anywhere from $200 on up.
If you look on pricewatch you can find new 9GB SCA drives for $15.
They only get expensive if you are looking for 72GB or 144GB drives.
Eric