I was in Japan last August and I found Akihabara very expencive with the retro games. In DenDen Town in Osaka there are more used/retro game shops than in Akiba and sell for less too. PC-E Duo RX's for 2000Yen with controller and cables. 600Yen for Super Mario Famicom games. and I can go on. Also more limited Edition stuff

And why did you take the Giza-subway line. A true Otaku takes the Yamanote-Line :P