How to evaluate the service "site support"?

Question

Technical support

Customers are increasingly asking for the service "Technical support site".
Those. for fix. a fee per month so that they receive such support (emergencies, minor edits, etc.)
Usually they make several tariffs of different prices and each of them includes a certain number of "hours of work".
That is why it is very interesting to know how to properly evaluate such tariff plans and maybe there are already approximate ones somewhere? All that I found is not entirely about the technical side of the site. I will be glad to examples, personal experience and just a constructive opinion

Answer 1

So far, the most interesting thing that I have found from the examples is anvexa.ru The
truth is that I did not understand what is invested in the concept of "hour" of work. You can insert a button for an hour) or you can write a plugin in an hour