Regarding prices for SFC games in Japan take a look at the pics below, I bought most of the games myself from Akihabara back in 2008 (you can see most of the price tags). I thought they were definitely cheap, I am wondering if they are still on the cheap side. I already had most of the games for my SNES (carts only mostly) so in the end I had a change of mind and last year I sold the SFC games and decided to continue my collection of NTSC/US and PAL games. It took quite some time in order to sell the SFC games and some SNES games in order to buy them again with boxes/manuals etc (and some extra money of course), but I would like to believe that I did the right thing, after all I 'd rather have the localized versions of my favorite games.
By the way I think that the SNES market in Europe is much more expensive than the US one, things in eBay are getting out of hand lately, and it is quite harder to come up with any good alternatives in most countries.