I would like to get a Lavalier microphone using with my Pana NV-GS400 ( or any other you would recommend to use for a interview situation, resp. recording speach of somebody who might be moving around in a documentation ).

Does anybody know which good Lavalier I could get in Japan? I believe they do have Audio Technica there. Is it realistic if I expect max 100 US$? ( I am a beginner, do not need pro equipment ). For situations the wire is a problem I plan to hook it up to a line in MP3 recorder. Is that a good idea? ( I don't have any yet, and there is surprisingly little choice of MP3 players featuring 'line in' )
I still think of getting a wired one for fear of interference and because of the prize. Or is there any recommendable wireless system for a small prize?

any suggestion much appreciated.

( I'd like to buy it in Japan where I also had bought my camera+accessory because there is much less selection in my home country Austria and ordering from the US many a times not only creates hassle with the customs but also comes expensive because of sending cost + 20% VAT on importing + import duty )