List it on Ebay and open it up to bidding. Start at say $100.
The market will soon let you know what it's worth.
A few years ago I sold a Durst 66 in super-good condition except for the lens, which was pitted, for $75. The 659 is newer and a much improved model with a color system, so may be worth more.
In my case, the new owner of my 66 still uses it and is happy with it. I am equally happy that an enlarger I used for many years has found a new home and a contented owner who still prints with it. Win-win.