Now I know this plays in a direction that you have tried to avoid - the assignment from the king - but it does seem to fit and even simplify your ideas. Think also that as a Ranger living (I assume in the Angle) before the events of 3019 then you would have already been under Aragorn's direct command and it is likely that he knows of you and of your unique skills.The Rangers have returned. We came back with them. And there is a king again, Barliman. He will soon be turning his mind this way. Then the Greenway will be opened again, and his messengers will come north, and there will be comings and goings, and the evil things will be driven out of the waste-lands.
Given the timeline you have decided on for Cimrandir then it's entirely plausible that he is one of the kings messengers. Who better to send than a Ranger capable of keeping the road clear who can also use his other skill set and begin the work of investigating the ruins of Arnor for the time when King Elessar casts his gaze northward?
Wandering alone in the wild, during sleepless nights under wet trees Aragorn would have laid plans in his mind for what he would do if ever his throne was claimed. Given how quickly he moves to cleanse the North and rebuild Annúminas (It seems within 50 or so years) he must have acted swiftly in sending people to the site with skill in such areas.
Bear in mind that there is no reason that this duty has to be a one on one special assignment from Elessar himself, he must have sent dozens of Rangers and other specialists back into the North.
As far as income goes it stands to reason that all of these messengers/agents of the king would receive some sort of stipend or later carry a letter of marque from the king (who by this stage has the treasury of Gondor at his disposal). He wouldn't want them having to spend days at the plough or forge when they could be out keeping the peace.