I spoke to TE fairly extensively today regarding the price hike.
The answer is obviously not as trivial as some make it sound regarding the AMOLED display. Of course it doesnt cost £400. But, as @Simon mentioned some posts above, they had to re-work the board and case in order to get the screen to fit into the chassis. Moreoever, they had to re-write the code for the graphics to display correctly etc.
I doubt they are doing it on purpose for their benefit. Old gear, trade tariff wars globally, shortage of certain components and time spent re-writing code etc… all adds up I suppose.
Anyway, I ordered one from TE direct to take with me on holiday. At these second-hand prices, may as well get one from the source with a warranty in case something goes wrong. Have to say that ever since selling mine a couple of years ago to a fellow 'Naut, I have missed the OP-1s immediacy and limitations.
BTW - the fact that the sequencer and synth buttons are switched on the Valentines Day promo is because they were shipped a unit that had the buttons assembled the wrong way around - yikes…!