That sporter stock really kills any collector value.....but that's kinda typical. In the '20's and '30's, surplus Krag's were really cheap, and made fine, inexpensive hunting rifles, so a lot of people "sporterized" 'em.
If it's a true Model '99 Carbine, the Serial # should be between 222,609 and 362,256.
I say "true Model '99 Carbine" because in the 1920's the DCM had a bunch of Krag rifles shortened to 24" and fitted them with '99 Carbine stocks, and also fitted with rifle stocks shortened to carbine length.
If your '99 Carbine were in original configuration, it would be worth:
Good (50-80% finish): $850
Fair (20-50% finish): $600