External eSATA enclosures other than the DX513?

Hi all, I have a slightly older 1512+ that I've loved for a couple years now. I have maybe 4-5 dissimilarly sized hard drives laying around that are too small to go anywhere else, so I was looking into getting a cheap external eSATA enclosure that I could hook up to my Synology and turn into a volume using SHR.

I'd love to have another volume to do backups to hold less critical data on. Of course I wouldn't want to expand the volume I have onto the external enclosure, but I was wondering if I could get something on eBay for ~$50-100 and get the Synology to join the drives on an SHR volume (rather than have the enclosure do all the RAIDing).

Anyone have any luck with anything similar? I'd like to avoid paying for the DX513 expansion as it's worth much more than the actual drives.

Thanks!