For comparison, I bought the Sinar DB-mounted barrel version of this lens (a more modern Symmar-S f/6.8 version) in excellent condition for $385 after shipping. I get so much use out of it in studio that I consider the lens well worth the price, although I might have paid a bit too much. So, lets place its value at $350.
Usually they go for about 150% to 200% of the DB price if they have a Copal 3 shutter. That makes it, let's say, a $700 lens if the modern S version in excellent condition. Now, take off a chunk of that because it is older, and take off a chunk because the shutter needs work, take off a chunk because you need to purchase the retaining ring, and take off a chunk because it has been dinged. Then, after all the chunks have been taken off, you might have a $300 lens (maybe). Bid 1/2 of that, or maybe as much as 2/3 or 3/4 if you are a risk taker.
Wow, makes my wife feel better that I bought A DB mounted 360 Symmar-S with a Sinar shutter (complete with cables) for $400.