I inherited a model 1898 in original condition about a year ago.  I have shot it twice since then, and will probably continue shooting it maybe once or twice per year.  Here is my problem: I would love to experience the vaunted accuracy of the old Krag, but my eyes just don’t work well enough to shoot a good group with the original open sights.  I am thinking of trying the Kraghaus 3-inch sight rail to temporarily replace the rear sight, but I do not want to spend a lot of money on a scope that I will rarely use.  So, can anyone recommend a cheap scope with long eye relief that will give good results with the 3-inch rail?  That rail is advertized at $38 including shipping, and I would like to spend no more than $100 for a scope.

I have the same eye problem as you do good sir.   I also have one of those mounts you are discussing.   A great mount and it allows you to mount a scope without screwing up the rifle.  I bought a Millett, long eye relief, variable scope with the German #4 recticle.   I works for me..... took two deer with it so far.   Didn't cost an arm and a leg either.

Definately Millett. If you dont like Millett, there is tasco, bushnell, or redfield. they all cost close to the same. The ones I suggested are under 200. From my experience stay away from the ones that are under 100 the value may be catchy, but they will never stay zeroed. Every bump and tap will knock them off. good luck and happy hunting