Special Order Option Pricing|Winchester Rifles|Forum|Winchester Collector

From what I’ve seen, one of the things that makes this hobby so cool, is that there were a lot of special order options available, and so there are a lot of different combinations out there. There’s also a notable lack of information on how much these options add to the value. I have a Blue Book and I subscribed to Gun Digest’s online pricing guide, and both are pretty vague and general on this, and they both advise having the gun appraised before bidding or buying. The Blue Book states that a rare option will increase a cheap gun’s value more proportionally than a high-end gun(might make an otherwise $800 gun worth $1000, but won’t make a noticeable difference on a $30,000 gun). That makes sense, but is there some kind of value guide(or even a rule of thumb)that will work when you don’t have an “expert appraiser” handy? I’m interested in buying a rifle with the double-set triggers, for instance. From what I have read(here, I think), that was something like a $3.00 option from the factory, and around 2% of the total guns produced had it. So, for a gun that would otherwise sell somewhere in the $700-1500 range, what would be a fair estimate of the increase in value? Thanks in advance for tips on this.