To get a true value on your gun, will probably take the services of a qualified appraiser.
Most sources give values for guns in various conditions, but none give values for guns with the original box.
The fact that your gun is:
A. A rare .22.
B. In 99% condition.
C. has the original factory box.
Increases the value over and above the normal ranges listed in the gun value books.
Few guns that old survive in 99% condition, and VERY few owners keep the original box a pistol comes in.
So, that your gun is in 99% with the box puts it in the "Unobtainium" category.
At auction, the actual price paid might be significantly higher than any published value.
An excellent source of true value might be Jeff Faintich at Faintich Auctions/Mid-City Gun and Coin in St. Louis, Mo.
Jeff was one of the 3 or 4 founding members of the Colt Collector's Club, and an internationally known Colt expert.