There is a fair amount of regional variation in price, but something in the neighborhood of $475-$500 would be a good starting point for a "book value".
If it's a -4 or earlier, with a pinned barrel and recessed cylinder, you could add another $25 or so. Also, the target trigger, target hammer, white outline rear sight, and red insert front sight would be worth an additional $75 or so.
Bear in mind that "book" is what a dealer would get. Trading it in to a dealer will usually get you about 2/3 of book value (maybe 3/4 on something he figures he can turn around right away). Private sales usually go for 80% to 90% of book value..... unless somebody REALLY wants exactly what you've got.
