Once again, JJ, good information and right on.
$275 - $350 average, without shipping.
If you can get it without paying for shipping, offer $250, be prepared to pay $325, if the engine isn't seized.
If the saw has to be shipped, it can be shipped in general around the 48 states for around $65. Florida to Vancouver might go $85.
I wouldn't call this saw in "excellent condition".
Issues are something not right about starter pull cord... where's the starter handle??... one link disconnected in controls (why?)... most of the original grey paint is gone... rusty overall and especially on the left side of the frame... internal condition unknown... (and how on earth did someone get the riveted-on Craftsman badge upside down?).
Pluses are: It has the chain guard (most don't); it has the helper handle (most do) and it is correct for this model Reed-Prentice 1200B (some I've seen have incorrect hh's); it's got the original scratcher chain, albeit rusty; and it does appear complete. Some elbow grease and a little filling-in can correct the rust pits on the frame. A paint job after going through all the mechanicals and this baby can look really fine again!
This one has the flat barstock brace underneath... the earlier ones had a rounded stock brace underneath. The very earliest ones had a spark retard lever on the bottom right, under the edge of the fan shroud. That was dropped early-on and this later one doesn't have it and wouldn't be expected to.
Engines were made by McCulloch Aviation. The 1200B number is a McCulloch engine designation. A few have an engine tag saying that, but R-P took that engine tag off most of them (and/or Sears).
See:
http://www.arboristsite.com/chainsaw/173584.htm#post2982874
Mr. BowSaw posted pix of his 1200B in that thread and that's what I would call one in "excellent condition". I was real lucky when I got my 1200B -- mint condition all-around and with extra NOS chain, tube of lube, chain links, manual, and other extra nos parts and tools. Cost me $285 BuyItNow and $65 shipping from Penneslynnessylyvania three years ago.
I do remember one of these selling for over $600, but I thought the buyer was nuts... a bidding war between two guys with low feedback... or a sucker and the seller's shill...
Also, a long thread on these saws in the history section in CSCF.