I’m sure you’ve already done this, and it’s all extremely approximate, but…
The homepage shows as around 1.76mb when I load it.
It contains around 1.46mb of images.
The assets all seem to be loading from Netlify.
At 60-80k per day visits, if the users were all new and cache wasn’t involved, you’d be using 105.6gb to 140.8gb per day, which over a 10 day period would be 1.05tb to 1.4tb.
So 815gb over 10 days does seem to be within the realm of the traffic reported.
Netlify have a general ‘Support Guide’ for reducing bandwidth usage here:
https://answers.netlify.com/t/support-guide-how-to-reduce-your-sites-bandwidth-usage-without-reducing-traffic/42768
I’m not sure what plan you’re currently on, but the ‘Open Source’ plan is likely available to Audacity:
https://www.netlify.com/legal/open-source-policy/
It may not make sense within the context of an Astro build, (I have no idea, I don’t use it), but you could host assets elsewhere on any other CDN that offers a lower bandwidth cost.
Or even use a competitor product (Cloudflare Pages) which still promotes ‘unlimited bandwidth’:
https://pages.cloudflare.com/
Their Astro documentation is here:
https://developers.cloudflare.com/pages/framework-guides/deploy-an-astro-site/