Information on the YAS 01 is hard to come by. It apparently was classified as a Q or MQ class instrument (this denotes origin, apparently Indonesia or China, but I am not sure about that) and sold a few years ago. It seems to be off the market. Some question whether it really is a Yamaha. In any case, it appears to have been at the very bottom of the Yamaha range. One opinion I saw said it was "a toy". One sold last August on e-Bay for $AU350.
If you are after a Yamaha, you might want to look also at Yamaha 21s, 23s, 275s, etc. They have a good reputation and could be worth the extra money.