Suggest the best cloud server for the news portal

I have a client and are planning to move to a server in the cloud with the automatic scaling function.

And they want to pay for the basic configuration and if more is required, then it must be scaled automatically. It is for the news portal and, in general, there are 400-800 visitors in real time and, at some point, they reach up to 40000-5000.

They have around 50 GB of total file and site developed in PHP with custom CMS.

Please suggest the best option and provider.