Ponitus Pilot
Sorry I was perhaps a little too brief in my reply, it was a long day.
ICAO is, as you rightly point out, a "specialised agency" of the UN. It became a specialised agency by virtue of a relationship defined in arrangements made between ICAO and UN Economic and Social Council under provisions of Articles 57 and 63 of the UN Charter.
The point I was trying to make is that ICAO was not set up by the UN but under an International Convention . Therefore UN Charter provisions on the availability of documents mention by df1 (if they exist) do not necessarily apply.
Having now double checked the pricing policy for ICAO documents is set by ICAO and contained in the ICAO Publications Regulations (Doc 7231/8, price $18!).