You should be able to find used SCSI hard drives for cheap these days. I got a 540 meg SCSI drive for cheap. Bought it used locally so I can't really say where a good place to get one would be. Search the net.
@elemental: pretty sure you can only use an IDE har disk in the emu not as a linked scsi drive in your pc but maybe i am wrong. Also read that the Emus have trouble with 7200rpm drives sometimes, 5400 is better i guess for these old machines :)
can i go as big as i want with these?
Pretty sure the max size for an internal SCSI drive is 18.3GB or something like that... not sure about the IDE internal setup...