geez, maybe I oughta write up a glass info tip!!
here's a bit about windshield lamination Fumblin, that talks about the latest material attributes
it\'s polyvinyl butyral , much different than the bad ol days
there's possibly only one [1] actual maker of windshields in the USA, which would be PPG, who started the biz before 1900, and have been responsible for most [if not all] the advances in the technology - they were the first in the world to get continuous conveyor mass production systems workable for volume production - there are prolly a dozen places in China, a couple in Korea, some in other places like India, the UK and EU and so on - in the EU the main one is Saint Gobain, who are big in all types of glass world wide, especially container glass, and are fighting with Owens Illinois for dominance - OI designed the machines that produce huge volumes of bottles automatically [hey, Ken Brown helped w/ that I think!

] and they've about sucked up every other bottle company in N America and prolly S as well
likely all the parts places get windshields from wholesalers who are stocking primarily PPG, but some might be getting offshore windshields, and all will be varying distances from the warehouse, and all will have different costing arrangements and different volume deals, as said above
shaped windshields like the 54 are not "cut to order", they are manufactured, and because of the compound curve [top to bottom + side to side] they are picky to get perfection to a pattern, and any mfgr wants a volume order to justify the setup and waste for something like these windshields - they'll note interest over time and make a certain quantity run, and not make them again until they're sure they need the stock - you'll find times w/ this sort of stuff [like w/ the 3.38 gearsets] where some or all of the vendors don't have them and can't get them for a period, until there's another volume run - making a single curved windshield to order would prolly run you a thousand or more, but there are places that will do it - in England anyway
the only thing you might want to ask the supplier is if the windshield is US made - the TF one was only put back into production a few years ago, and I'm sure it's US made, and perfect - it's also available thru any local auto glass place [which is a good indicator it's PPG], and you might check if the 54 is as well - otherwise between vendors w/ US made glass, you'll hafta compare the shipping cost and the vendors reputation and toss yer own coin!
the 5-9 TF windshields are more expensive than the 54/5 AD ones because the sharper bend is more troublesome, and the 60-63 is more expensive yet [although about the same size/shape] because there's less demand, less volume - the rear TF big window is also being made new now, and it's tempered not laminated - also note that the majority of windshields anyplace will have the tinting band at the top, or be entirely tinted, and that tint is in the core laminate, not the glass - don't know if that's because everybody wants that or because the suppliers thought they'd want that and the clear ones sold first!!
Bill