I am planning to turn on Log delivery for my set up. Will I be charged for getting the logs delivered to my S3 bucket?
No charges from Fastly. As mentioned in our docs  we don’t expect the log traffic to be vastly more than the request traffic, and this is the case for the majority of our customers.
If you had quite a few logging endpoints for a service this might be true.
On the Amazon side, it looks like they only charge you to get data out.