Hmm, that's probably a bit on the pricey side, but it obviously depends on its condition and how much you want a dual record auto reverse deck with lots of features. Also, the price depends somewhat on the availability of stuff in your country.
I've noticed on forums like this that most "cassette head" audiophiles tend not to put auto-reverse or twin decks at the top of their list. :thmbsp:
However, these decks have handy features, with probably the chief one being that it has dual record with a relay function, which allows you to record for hours at a time.
I had a well-worn one of these a few years ago, that I bought from a pawn shop, and found it a bit slow a clunky. I ended up using the timer-record function to record long radio shows until it died.
As far as their best decks go, you can have a look through this list.
http://www.vintagecassette.com/Yamaha
Many of the decks on this site have the original recommended retail price.
It looks like the KX-690 is/was a nice deck, with 3 heads and 3 motors.