Impossible to answer without a detailed description of all markings, features, barrel length, sights, grips, box, papers, accessories, condition, type of action, etc..
You can get a letter from Colt.
100 to multiple thousands depedning on specifics
50-500 usd
The Colt 45 was called that since it was made by the Colt company, and fires a .45 caliber bullet.
Proofhouse.com has Colt sn data.
made about 1920
Proofhouse.com has Colt sn data.
Don't know the value ,but a Colt 1908 hammerless .25 semi-automatic with that serial number was produced in 1921.
Proofhouse.com has Colt sn tables. You can also call Colt and they will tell you.
Nice small semi-auto that is collectable.
trade it in for a 45 caliber
about 1921