Also, how do you usually list a rifle shipping/ffl costs? What's typical?
You can do it several ways. Taking FFL cost + an approximate cost works. Listing it as "actual shipping cost" is nice, but so many try to weasel out of said, so a fixed figure is better.
Shipping costs vary according to distance. Insurance costs vary depending on the amount covered. If you post a fixed price odds are either you or the buyer are going to be cheated. If you post the shipping weight, the buyer has no cause for complaint; he can check the shipping cost online just as well as you can.