There's plenty for sale, but Speed Kings hardly were sold in Everett. I think I bought one, a GMC 'Screamin' Jimmy' cement mixer. Anyway, in this condition, it runs about $12-20, depending on who you buy it from.
We discovered a cool gift shop that we HAD to check out and I found this wagon model kit. I was surprised at the size of it. It was very tempting but I passed on it Is this a fairly common model?
1/16 isn't too common. 1/25 or 1/24 is by far the most common scale for automobiles. I remember seeing a 57 Chevy in 1/16 scale when I was around 12 years old. I wanted it so bad But I was traveling with family friends, so I didn't have the money and it wasn't like I could just come back after I mowed a few extra lawns..
1:18 is common for diecast. 1:16 is unusual in my experience. Matchbox Speed Kings had some great models. They had a shooting brake Corvette that was one of my favorites when I was a kid. I may have to buy another one.
1/16th and 1/8th scale models are no longer made, IIRC, so it *can* be rare. In junior high, I got the 1/8th scale 1965 Corvette for my 12th birthday, and that was really cool to put together. I even gave it a 'fuzzy' interior.
That Speed King Vette and boat on trailer should be around the same scale as my Monaco wagon I bought recently.