Dear Mark,
This is a tricky one of course but if we break it down I think it could be done. Looking at the novel let us suppose there are approximately 30 locations worthy of a plaque of uniform size and design (say a circular blue plaque 50 cm across, with the name of the location, a brief explanation of its role in the plot of Around the World in Eighty Days, the number in the journey /sequence of plaques, a unifying message in world literature and the name of the organisation / individual that made the plaque happen).
From looking on the internet I think a good quality plaque would cost $1,000 - $2000, but their inherent uniformity and ordering 30 plaques may not necessarily cut costs but allow one of greater quality and durability. So the cost of the plaques (which can theoretically be designed online) would be perhaps $60,000. These would then be 'donated' to the relevant locations in say a dozen countries and I think you would have to add and extra $,1,000 - $3,000 to facilitate their mounting on a suitable building or a simple donation to a local charity. this would give a total cost of the project of say $150,000 to $200,000.
I know the BBC did a similar scheme, this is from A.I.
To mark the landmark documentary series Black and British: A Forgotten History, the BBC created and placed
20 plaques worldwide. These plaques were installed to commemorate significant, often overlooked sites and figures connected to the history of Black people in Britain and the transatlantic slave trade. [
1,
2,
3,
4,
5]. The BBC did not publicly disclose the specific manufacturing or installation costs for these individual plaques, as they were produced as an integrated part of the historical research for the broadcast series. [
1,
2].
For organisation and funding, I think there are several avenues.
The United Nations through UNESCO, core initiatives and the Creative Cities of Literature Network - good at international cooperation but they will have other funding priorities.
The French Government - depends to what extent they are supporting the Verne 2028 celebrations and whether they would want to have a global input. However Macron's dog is called Nemo, President Macron is from Amiens and one of his favourite books is 20,000 Leagues Under the Seas.
Different Verne organisations...not any Verne organisation per se but an individual in those one of those organisations (perhaps a member of this forum) who would act as a sole benefactor and bequeath a permanent memorial plaque which would then bear his name in 30 locations worldwide.
Crowdfunder on the internet.
Personally I believe the best way forward would be an individual benefactor (quick funding to give the scheme instant viability), then an appeal to Macron as the best avenue to get the scheme rolling for implementation in 2028 (only 18 months away). Macron could then work with UNESCO to iron out all the political red tape that constitutes putting up 30 plaques in a dozen countries.
The kickstart could well be this forum. Somewhere out there may be a rich benefactor who for deeply personal reasons would wish to kickstart and pay for the scheme.
To be honest if funding was already there, then I think it would be very straightforward as in the BBC example given above.
So I think a philanthropical donation and then Macron might be your best bet (having said that Macron might be my best bet too!).
Best John