Looking at my copy of Flaydermann (which is 10 years old) I see a 2001 price guide of very good = 225, excellent = 350.
Even allowing for general increases over the last ten years, the 300 for what you describe seems a bit borderline. The woodwork for the "long" Nagant will not be as easy to find as for a 91/30, and you will either be replacing the lot or doing some cutting-and-pasting of the fore-end. And the chances of finding a set of Remington wood at a price that makes sense are poor.

The only time I saw a US-made Nagant here it was a Westinghouse, and the dealer wanted 400 Euros for a rifle which was in very moderate condition. In other words, if it had been a normal Russianicon model I would not have looked twice. Prices where you live will be different.

I suggest the following way of evaluating it:
1) If you are just a collector, forget it. Whatever you put into it will not make it original again. Unless you find a set of Remington wood - and that would probably be uneconomic.
2) If you are primarily a shooter, and confident of your luck and your D-I-Y skills, you could buy it, but do not pay more than a normal Russian-made example would cost in the same condition.