Sorry Scott, but you will not find a cheap SCSI card that will work with both OS X and a DLT.
SCSI and OS X have never worked well together, and only the expensive high-end cards work good, if at all.
Cards from ATTO and Initio both work well, but at a cost.
Of course if you have a DLT, money may not matter. But if it does I'd suggest looking for another backup medium.