This was from a Postal Commemorative Society cover. Value is a virtual 0. You can get these covers on eBay for under $1.00 each
Sorry, revstampman, you are 100% incorrect
, this was a proper postal issue. It was NOT a fake gold foil stamp by the PCS, the covers of which are "worth" in the range of $0.00 to $1.00 as you noted.
The clue you seemed to have overlooked is the full Scott listing of the item as C309 which pictures then President For Life François "Papa Doc" Duvalier whose rule was take over by his son "Baby Doc" (Jean-Claude Duvalier) in 1971 until being over thrown in February 1986.
For me, the stamp raises many more questions. Was it ever distributed to post offices? What possible need would a stamp of this face value fill? How would postal employees ever keep track of them, since they are single, small items?
Knowing very little about the Haiti and its postal system, I suspect that these stamps are 100% philatelic; they were never intended to be used for postage.
Of course the information is out there if one bothers to look. But be helpful asking veiled rhetorical questions in a manner to completely discount the stamp. The issue was not "100% philatelic," but rather a fully 100% narcissistic issue by "Papa Doc" to honor himself.
As to postal handling, back in 1968 there was not much demand for the post office due to the abysmal literacy rate which belies the concentration of the literate in the urban area while pumping up that of the rural areas. By 1982 the literacy rate had rocketed to 34.73% and rose each year there after (ignoring earthquake years) and resides in 2022 at something over 61.69% as determined by the World Bank in 2016.
The 30 G (gourde) paid the exact surcharge rate which was required over the first surface rate to qualify for the first airmail rate going to the USA. I do not have the airmail surcharge rates from Haiti to other, non-USA, countries but it is unlikely the UPU forced much variation on the financially poor country.
Scott lists the stamp in the 2022 International (vol. 3B), with no qualifications nor footnotes, at $40.00 mint and $50 used. That is far above the values of other airmail stamps of Haiti within months of issue before or after, these values belie the scarcity of the stamp, mint or used and especially on cover due to the huge lack of current interest in Haitian postal emissions.
Currently, there is one mint listing on eBay USA from a British seller with a price of $29.79 with an added $3.51 shipping, well consistent with the current Scott mint price. I don't think there is likely much of a premium for the FDC (unaddressed) but expect a huge
premium for an example on cover which travel in the mail stream.
For those interested in US International postage rates between the USA and other countries (that is both outgoing or incoming) they can be found
U S International Postal Rates 1872- 1996. Anthony S Wawrukiewicz, Henry W Beecher. Published by Cama Publishing Co, Portland, 1996 [1st and only edition]
U. S. Domestic Postage Rates, 1872-2011 - Third Edition
by Anthony Wawrukiewicz and Henry Beecher (2011, Hardcover) 3rd edition published and selling originally by the APS.