The increase doesn't look too large, but if you need a similar alternative I like Vultr a lot, the Neocities CDN is hosted there and it's been rock solid performance for years, and it's quick to get access to competent tech support. I wish I had more infra hosted there actually.
Not sure the underlying economics here for DO or their motivation, but I don't think DO can expect to their customers to react to this the same way customers are reacting to inflated costs in cars, groceries and the like. If other providers follow suit, maybe that's a sign of slowing efficiency in the hardware, end of Moore's law, etc.
[0]: https://www.backblaze.com/blog/wp-content/uploads/2017/07/ch...
Usually - well before inflation - this tier was $2.50.
EDIT: I just saw your comment clarifying that you were speaking about Vultr. That wasn't clear from your phrasing, but I wanted to acknowledge it here.