Best Places To Purchase Boat Passes?

So I noticed that TP scrolls and Boat Passes cost more depending on where you're buying it. For example, it only costs 8E for a Ragni scroll in Ragni, but 26E in Nemract. This all makes sense, but for Boat Passes you can't buy the Boat Pass for the place you're at. So what are the best places to purchase Boat Passes for all the islands and whatnot?

 

The wiki has price listings for all major Seaskipper ports. As for minor ports, I know you can get Nemract passes for cheaper than 12E at certain places (e.g. Durum) so that may hold for Selchar and Llevigar as well. Also of note is that's it's cheaper to go Nemract -> Selchar -> Llevigar rather than Nemract -> Llevigar directly.

TP scrolls I think cost the cheapest price at their own location, and a similar elevated price at every other location that also sells them.