How do you handle the bandwidth costs? These are probably a negligible proportion of the costs at the scale of an Instagram, but hosting providers still have a big profit cut at smaller scales.

For example, I could host all my images directly on my Linode, but the cheapest Linode has only 1 TB of outbound transfer a month (for $5), and over quota you're actually charged more than that, $10 / TB. That comes with only 25 GB of storage. They'd also probably be pretty slow for most of my visitors, since they're hosted on a single server somewhere in California.

If you want faster distribution around the country and globe, you might consider S3... that same 1 TB of data out is going to cost you $90 / month.

Meanwhile, it's clear the REAL costs are not that high. Flickr Pro is a mere $5 a month, with the same high quality (uncompressed) photos, and a global CDN. You can store an unlimited number of pictures with Flickr Pro. This is already way cheaper and faster than anything I can set up on my own, as far as I know, and SmugMug is still making money off of this, presumably, enough to cover their free tier.

I've been slowly piecing something like this together for myself using jekyll. I'm not familiar with the tools you're using, but the demo site looks very nice. Good job!

Are there other examples of turnkey self-deployed sites like this?

I'm actively developing my personal site which is built with elixir and phoenix. That said if you are looking for an out of the box solution I would stick with simple and go with a static site generator like you mentioned or possibly Wordpress.

Also this is one of the big reasons I really hope activity pub takes off and people start to incorp it directly into their own sites.