I've bought mine at
www.ereader-store.de, too.
Fast delivery, after being in stock (I preordered) and - as mentioned before - Booxtor is really active in this forums. This is a big plus, as he - as a seller - has a more direct contact to Onyx International and really takes the wishes of his customers seriously. He is e.g. in contact with Onyx International regarding an appropriate stylus replacement, as charging $20+ for such a tiny plastic "stick" seems just silly.
However, since we do not know where you live it's hard to answer whether ereader-store.de is the cheapest. Considering Europe I'm pretty sure, since the M92 is offered for 400Euros elsewhere (354 now at ereader-store.de). Living outside of europe may change that, since you then would have to discount the german taxes (then ~307Eur) but add increased shipping costs (see
http://ereader-store.de/en/content/1-shipping) + taxes of your homeland + currency conversion.