I haven't thought of buying it online in Japan, the websites are usually available in English as well? Anyway i think ebay is more convenient if you don't want to pay any tax (there's always a risk though but i haven't been caught yet!).
I just went to the site now, and priced an AD900 shipped to France for 23,300 Yen incl. shipping which converts to 180 Euros roughly (and $240 USD which is I think about what I paid 3 years ago). You'd probably still have to deal with customs.
Yep eBay is definitely a good option. But usually its dependent on the seller going with your requesting them to declare a lower value Although, it's odd, sometimes I've been taxed and sometimes I haven't, guess it depends on customs if they feel that it's a taxable item or not. I know some items (at least here in Canada) don't get charged duty, prescription eyewear I believe.