Dropbox's cheapest plan that I see on their website is €11.99. My VPS costs me $5 per month and runs Nextcloud with no arbitrary usage limits, as well as tons of other shit I need for different things. I assume it's the same for OP.

My VPS (Digital Ocean) gives me a whopping 25GB for $5/month. Are you saying you can get a TB or more of storage included with your VPS for $5? Please tell me where!

I've been using a Google cloud free-tier VPS with Syncthing and it works great; I imagine Nextcloud would be similar. I do backup my instance with snapshots, which aren't free, but so far cost me about $.01 per month. Note, Syncthing doesn't actually require a server, but I still find it useful for offsite backup.