Book Off in NYC has the original prints of the manga in Japanese. Was just there less than a week ago so they should all still be there! While there I also scored the Nakayoshi R season Anime Album - for $14! and the Kodansha Anime Series Picture Book Vol 6, "Sailor Jupiter Arrives" - for $3! And as I recall, the Sailor Moon manga are in the $1 section so you could get most of the manga, most of them first-prints with posters, for pretty cheaply.
Kinokuniya on Avenue of Americas has the new Kodansha prints, plus the Japanese re-prints from 2003 if you wanted to pick those up.
Also if you hit Chinatown, in the Elizabeth Street Underground Shopping Mall there is a store selling bootleg Usagi plushies - and another store selling the new wallets, keychains, etc.