Like most things, you should try and sell it for what you feel it is worth to you. The Yunker 1 and Yunker 4 are of no use to anyone who wants to make them more powerful. To my mind the Yunker 2 and 3 are the desirable ones.
IIRC I sold my Yunker 3 for £275 but it was very desirable and had many upgrades.
HTH