For one popular project of mine that hit the front page I had a 2% sign-up rate. It was a free service that used GitHub for authentication, which likely helped.

I had a Netlify landing page (CDN), and the web app was a Django app on a single DigitalOcean droplet. I didn't see any complaints of performance issues / resource usage stayed low.

That sounds like my preferred setup! I use a static site deployed to cloudfront backed by a Django app on Digital Ocean :)

It might not work for all applications, but it tends to hold up great against traffic spikes and the hosting costs stay in the low teens (USD)!