Etching aluminium might not photograph with enough contrast to pull out the QR code.
Laser etching glass might be worth a look. You can increase the contrast fairly dramatically with black paint, which can be cleaned and reapplied without damaging the glass.
Is it 1-2kB uncompressed? Because compression will help, the smaller you get the data the larger you can make the QR pixels. You can also split it into 20x100B chunks, and then as long as you number the slides you can rebuild later.
Also, ecc-h only gets you 30% recovery, duplicate or triplicate slides could increase that even further.
Rtx3050? Should be supported for a little while, and seems to be around $300AUD. Probably still overkill for a NAS though.