You got a couple of really nice block planes for $15. Your Sargent #5206 was manufactured between 1913 and 1947. Based on what I see, the iron on the plane and the rest of the parts appear to be consistent in age and wear. During its 34 year production timeline, the #5206 was produced in at least twenty different versions. So, there's a pretty good chance that the iron on your plane was accurate for one, or several, of those twenty or more versions, and therefore original to the plane itself. Unfortunately I don't know enough about Sargent planes to tell you where your plane fell on the production timeline.
The Stanley #118 was produced beginning in 1933, and continued well into the 1980s. On most occasions, Stanley's competitors, like Sargent, copied Stanley's designs. Here's an instance where Stanley copied one of it competitors. Stanley finally started making a steel block plane twenty years after Sargent began producing its #5206. I noticed that your plane has its model number stamped on its left side. Stanley started stamping model numbers on various block planes somewhere around 1947. I think it's safe to say your plane was produced at some point after WWII.
Finally, I don't usually like to talk about the price paid for hand planes and antique tools, because a reasonable price to me, might not be to someone else, and vise versa. That being said, I think Kaune's website is a nice resource for looking at various planes, some rare, some a little more common. However, I think his stuff is generally priced on the high side of reasonable, and more often than not, just plain overpriced.
Jim C.
