I've spent a few years ordering things online from Japanese stores and am used to paying Japanese prices + postage + custom charges so to be able to pick things off the shelf and not worry about postage or customs made everything seem so much cheaper!

I also took the approach of thinking exclusively in yen when I was there. Instead of converting it into pounds I looked at it as "I have xxx yen left so I can afford to spend xxx yen on this". Otherwise I'd have had a heart attack after hitting the tour goods stand haha.