ok, the solution mentioned in the article below for pci-x is for a 4 or 8 disk raid system:

- SeriTek/2eVEN4 4-Bay External eSATA Enclosure Bundle with 4-Port Host Adapter - 630$
- 4 Raptors 74gb - 644 $
total ± 1300$
double that for read&write speeds around 400 MB/s and more storage, of course.

still hoping to find a solution that would provide a bit more hd space than the raptors ..