I currently have 22 websites online (including this own), with a monthly cost of 10 dollars (around 40 reais).
This is not possible on shared hosting like Hostgator or Umbler (which I use for email).
As I have a good knowledge of Linux, the Digital ocean (in this link you get 100 dollars credit card) is and always has been a great option, having great and extremely reliable VPSs. Besides the very low cost, and you can do whatever you want with them. I've even used it as a TeamSpeak server, for example.
Currently with my setup, I have a cost of about 2 reais per site, and with time off. Of course, considering they aren't giant sites, but if they do grow, a server upgrade in Digital Ocean is done with a few clicks.
Server configuration can be done manually, or with a manager such as ServerPilot ($ 10 credit on this link). It costs $ 10 a month, but it's worth a look at the current plans.
I highly recommend it because it is extremely easy to get a new application to run, especially if you use WordPress.
It also has a dashboard to help with performance diagnostics.
Relying on cache plugins, you can easily have dozens of sites with thousands of hits. All this with just a $ 5 VPS, no problem at all.
There are alternatives to ServerPilot, such as https://runcloud.io/, but I never got to test.
I am available to answer any questions about the services, your comment is welcome!