Do your research first. I’m assuming this is a Sea King brand that was sold by Montgomery Wards, but there were other Sea Kings out there. Evinrude made a line of outboards they called the Seaking lineup in the 1950s, so figuring out exactly what you have is key.
Then find out exactly what year it is. I believe the first Sea Kings were from the 1950s, but the brand was made all the way up into the late 70s or early 80s. From my recollection, these motors were made by a variety of companies, the best known one being Chrysler, but that was not the only maker that made them for Montgomery Wards.
What it’s worth will vary from nothing to hundreds depending on age and condition.
Some of the later models can be “worth” a surprising sum IF you’re willing to part them out. The cover alone could be worth $100, the block/powerhead could also be worth $100. It just depends on how much work you’re willing to do to sell it.
Grouse