It is vague and you are not the first to be puzzled. When I did my research I found this blog post helpful.
Assume you are talking about Custom Search Engine (terms you noted in your Q) and NOT Google Site Search (paid from the start). The reason I ask is that the XML function is only for Google Site Search customers. There is the JSON/Atom API and Custom Search API available for CSE.
For Q1, one Query = one request. You can use as many keywords or other parameters in your request (see comments in the blog post I referenced), but you will always be limited to 100 results.
For Q2, the billing is enabled through the API console. Once enabled (and in order to allow the 101st query) your code must include both your cx and API key. So in theory you could set up multiple search engines within your API and stay under the 100 request limit, but I have not seen a way to allow an API to support multiple cx keys.
Answer from edswartz on Stack OverflowGoogle Custom Search Engine pricing - Stack Overflow
Why people are paying for API to do google searches? Why people won't use simple Python scrapy/requests script instead of paying 200 dollars for 200k searches?
Google Places API new pricing. From $0 to $2,180 per month??
Why is Google Maps Platform API's pricing so ridiculous?
Videos
Hi. I am going currently through different SaaS's things and I found business that is selling access to API to do google searches. And I don't understand who is paying for this.
First of all, I thought that google is selling access to their own search through their own API, but apparently it was deleted for some reason?
Out of curiosity, I checked out how hard it would be with Python and Scrapy and it is around 10 lines of code to get search response from google.
I am wondering what am I missing? I was thinking about 2 obvious(?) problems:
How well would Scrapy/Requests with let's say FastAPI scale. How slow it would be.
How much would google tolerate. I can only guess that if 1 ip will be making new search every 3 - 5 seconds non-stop. Google would ban this ip. So the more requests, the biggest IP pool would be needed?
But other than that, what am I missing? Why someone is paying 200 dollars for 200k google searches?