So I am a bit of a Krag afficianado, but not a serious collector. I agree that you may have an 1898 carbine and it certainly looks cosmetically right, although the overall length appears to be out by about an inch, which could point to a Bannerman or later "conversion". It also looks to be in good condition. For some reason, I cant get the second set of pictures to open for me, so I can't tell if it has the correct front sight. If it is an original 1898 carbine, it would probably be viable in private sale at $1500 - $1800. If a later conversion, somewhere between $500 and $800.
As Stamps6 notes above, these can be great shooters if the bore is in good condition. Barrel groove dimensions had a fairly wide tolerance, as in .308 - .312, so slugging the bore is an important step to understanding how to get it to shoot. I have an 1898 rifle that I shoot in local competition. Mine is tight at .3085" and, with the Lyman 311284 210 grs RN bullet at .310", it is a very accurate rifle indeed. Also, while people make much of the weak one lug design, that is relative to modern 60,000 + psi actions and cartridges. The B&C record for elk was held from 1899 to 1968 by John Plute who scored with 30-40 Krag. Elmer Keith wrote highly of the 30-40 with 180 grs bullets as a deep penetrator on elk. In the world of internet hunting today where most deer and DRT with one shot of a 6mm bullet at 750 yards, it is easy to forget that the 30-30 did yeoman's work killing deer and elk for many, many decades, and that 180 grs at 2350 is an extremely effective elk round out to 250 yards. In fact, I will be using a Win 1895 in 30-40 for elk this coming October.
So, while I would not suggest that your Krag is an ideal hunting rifle, were you so inclined, it is a viable and fun rifle for iron sites shooting.
To determine whether it is an original carbine and get a precise value, this is the place to go:
http://http://kragcollectorsassociation.org/