When working out how much to charge for the prints, I do the calculations (of course) in Japanese yen. So the yen price for these prints is the 'base' price, and the others are calculated from that.
But because currencies fluctuate over time (do they ever!), I must sometimes make adjustments to the prices that you see here. I have no idea when such changes will happen: perhaps tomorrow, perhaps not for months.
The price that will be in effect for the duration of your subscription is the price showing on this page at the time you send in this form. I may be sticking my neck out a bit farther than I should, but I will guarantee that price for you for the 18 months, even if your chosen currency falls against the yen.
But let's be fair about this. If the currencies go the other way, please don't come running and ask for a discount! :-)