> how much money can we expect e.g. Google to spend verifying court orders targeting users on free plans?
You don't pay money to enter Walmart but they are required to spend as much money as it takes to ensure you don't die in a fire while giving them zero dollars. Likewise food safety standards required by law aren't a sliding scale based on income. The relevant factor isn't how much money you made off the mark its how much harm your behavior can cause to that person.
If you put yourself in possession where your failure causes them greater harm you bought yourself a potentially expensive obligation that you wouldn't have for example if you just served search engine results based on search query or ads served without knowing the persons life story and the contents of their diary since the 3rd grade.
The actual answer is however much it takes to do a reasonable job or we ought to just fine you so much per screw up that you are forced to go sell shoes instead of search engine results.
The government can and should help make this procedure reasonable as it is 99% of the problem. Such orders ought to be cryptographic signed by hardware tokens that are physically in the judges possession on a device that isn't online THEN emailed to google. This relies purely on 1970s technology and probably should have been implemented about 20 years ago if we weren't collectively complete morons.
While this is implemented just coming from judges official government emails as opposed to their personal emails or a billion idiot cops would be substantially more secure.