I’m not sure I would bet on the web itself still existing in 100 years. That being said, I think the biggest risk here is your hosting company going out of business, or changing their products such that they won’t host your site anymore.
If you’re OK with your website having a big ugly URL (which might not be a problem if you use a QR code to point to it anyway) then hosting a static website on AWS S3 might be your best bet. There’s so much money flowing into AWS right now, I imagine there will be enough interest to keep it going for several decades to come.
EDITED TO ADD As far as i know you can prepay your AWS bills, so you could prepay a massive amount and hope it outruns future price inflation
Edit: others are pointing out that it’s only free for domains with fewer than 10 pwned addresses. I have 8.