ah, I see what you mean. If they were all produced and sent to Ireland a while ago (say a couple of months) why are prices being amended now?
Well without being privvy to the exact details of MM accounts and contracts there could be several reasons. Payment terms could be one, if MM are not paying all up front and have structured payment it may be a consideration, possibly unlikely though given the nature of smallish companies dealing with Chinese giants. Most likely it'll be up front or 50:50 type arrangements.
Or it could be that overall business is being looked at and the profit margins now need to be increased to allow funds to be set aside to go towards affording the next run, which could already be at a planning / prototype stage and require funds to progress.
There could be other considerations, I don't know the specific industry well enough to comment specifically on it. But note as well that Chinese minimum wage is set to rise substancially this year and will be a big impact on production costs too.
EDIT: Just re-reading the blurb from Murphy:
"".....due to the currency exchange situation between Euro/Sterling and Euro/Dollar we are having to increase prices on all new stock arriving in as we cannot afford to absorb these price rises.""
To me this could imply that there are several runs of various stock sitting at the manufacturer, stored at factory rather than stored in Ireland and if MM only have to pay on release of shipment then that would certainly impact the pricing of the current runs against those previousl shipped even if all produced at the same time initially. This would make sense production wise I think. Lets take the mk2 as an example and say that all liveries were produced at the same time for the same cost and have sat in storage in China since, with MM only bringing them in staggered so one livery is sold before the next released. That would mean that initiall the cost of the Galway / IE / Supertrain was all the same. But with the Supertrain only just release the FX rates will impact it now rather than at production and cause the price rise. If say there is also an IR livery next up in 6 months the price could rise even further if FX rates continue in the same trends.
Again I'd just like to point out this is all speculation based on my general business experience and may be off the mark entirely, it's just what would seem reasonable as an explanation to me .