Here's some help on the models:
The New Service Target was introduced in 1900 and discontinued in 1940.
A top frame that was lightly stippled, a checkered trigger, checkered grip straps, and adjustable front and rear sights.
Before 1913 it had black, hard (Gutta Percha) rubber grips with molded checkering and Colt logos, after 1913, checkered walnut with silver medallions.
It came in 6" or 7 1/2" barrel, and in .44 Special, .45 Colt, and .45ACP.
The Shooting Master was made from 1932 to 1940, in serial numbers from 333,000 to 350,000.
Front and rear adjustable sights.
Top strap, and frame back were all stippled.
Trigger and both straps were checkered.
The butt is slightly rounded, where that was only a rare option on the New Service Target but the square butt was an option on the Shooting Master.
It was first made in .38 Special-only, but .45 Colt, .45ACP, .357, .44 Special later.
It was only available in a 6" barrel.
Problem is, they look almost exactly alike.
Problem with placing a value on these is, first, Colt prices have blown the roof off and gone into low-earth orbit.
Second, these Colt pre-war Target revolvers were never really common, and are much less so today.
As usual, condition is everything, and excellent examples will bring high prices, but how high is anyone's guess these days.