If you were just looking to put all those IDE drives into service and wanted to mirror 'em for the protection that offers (no it isn't a backup, but it turns a hardware failure into a low-excitement event - and if the drives are old...) why not just get a IDE controller?
Like the promise ones (here's a quick
froogle search). The IDE 100 ones start around $10, 133 around $40 (no idea how old your IDE drives are so 100 might be fine. I've used these in setting up mirrored storage in family file servers (high speed not really necessary - mostly just lots of media files) and they're fine for that.