I found prices to be somewhat cheaper overall, with some good deals to be found if you know where to look. Tsukiji shops don't take cards with the exception of aritsugu (don't know about the nenohi shop at tsukiji, it wasn't open when I was there last November, but they probably don't take cards either). Some of the shops in kappabashi have decent selections, and will take cards, but going to the specific brand shops is more fun.

Best to just bring yen.