Welcome to the forums @tval. Glad to have you on here. I think @BANKS has already offered excellent advice. While I personally have not travelled to Japan, I will agree about Mercari JP. I think the prices for Japanese stuff has really lowered/stabilized and you can find deals still, well relative to the markets. Just be careful and do your due diligence about the listing and seller before purchasing.
I would also recommend this thread by @genchiro.
I think they have done a great job in documenting the store prices with lots of pictures so you can have a look. You can also check their last trip which has a lot more pictures and also a summary of the travels. I think it should give you a good indication about the cards and pricing when travelling.
Wishing you good hunting and safe travels and a fun time in Japan. Do also post your pickups after you are back.
Cheers!