You want a backup-device?
Well,... I'd suggest you to get the software for free and installed (FMCB and OPL) and don't waste your time with the incompatible commercial stuff...
Btw.: It isn't as cheap as you intended, but depending on your PS2-Type you can use a NAS/PC without any extra-stuff... (beside the software of course)
I just got a 1TB-NAS from 'Buffalo' for 99€ (and I allready saw it for the same dollar-price).
I intend to compress the installed PS2-Games/PS2-ISOs (but not the VMCs), so that I could gain even more (space and features) out of my NAS.
Loading games from USB, isn't quite funny on a PS2.
FMVs might stutter and the compatibility isn't as high as on SMB (I suspect it...).
If you use a NAS, you can load your games from it; read/write to VMC on NAS and don't have to worry about file-(de)fragmentation for USB-Devices (if used by OPL, or PS2ESDL).
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux