I have noticed a massive price issue that happens and a cost to the user if purchasing using steam to buy things,
for example the rate for gaijin coin is including tax £1.31 - 1 coin. If bought through steam.
£0.94 - €1 - 1 coin through paypal or normal card.
So to save yourself some money loss caused by steam use the gaijin website and pay through there rather than steam.
pictures attached for example