Offhand, I'd look into NearlyFreeSpeech.net (free when you have no traffic) + CloudFlare (lower the cost of a spike in traffic). But I don't know whether e.g. NearlyFreeSpeech allows you to not use their dns when hosting a site with them.
Downside: two business points of failure.
How legible would a QR code carved in stone be after 100 years? Would anyone, even a Google Glass---esque cyborg, realise what a QR code was?