No. Again, there is opportunity cost. Opportunity cost is always there unless you have no other choices. And I don’t mean the other choices are bad or undesirable, simply that there is a single choice.
So for example you prior post that discusses an account with 3 alts. Opportunity still applies. The fact that I can use 2 alts for PI does not remove opportunity cost. In fact, there is opportunity cost there too. That you skilled and are using them for PI means you incur the opportunity cost of the next best option. And there is still the opportunity cost associated with AFK camping that I noted. That you have income does not remove opportunity cost.
You can find the definition of opportunity cost here.
In microeconomic theory, the opportunity cost, also known as alternative cost, is the value (not a benefit) of the choice of a best alternative cost while making a decision.
As I noted, so long as you are making a decision–i.e. a choice between two or more choices, then opportunity cost is present.
A choice needs to be made between several mutually exclusive alternatives; assuming the best choice is made, it is the “cost” incurred by not enjoying the benefit that would have been had by taking the second best available choice.
We satisify the mutually exclusive aspect by noting that if you are AFK camping you are unable to be somewhere else in the game with that character (or any of your other characters). So in your 3 alts on 1 account example, if the person is going to AFK camp 23.5/7 then not only is the opportunity cost the cost of what ever else you could do with that alt, but also the ISK income of the PI alts.
This concept is old. Ben Franklin had a glimmering of the idea with his famous quote, “Time is money.” Frédéric Bastiat gave the first articulation of the concept although he did not name it. It was Friedrich von Wieser, the Austrian economist, who came up with the name.
There are other things you are giving up again. Suppose I have trained my camping alt to also have PI skills. Travelling back and forth now means I have to give up camping…which is an opportunity cost. Second, choosing PI over say invention means I am incurring that opportunity cost as well.
Further, travelling in a cloaked ship is when such ships are most at risk of being destroyed. So with 25 alts there is now a non-trivial probability that one or more of the cloaking ships will be lost.
So, no, after they AFK it is not cost free.