Assuming that the rifle has all USGI parts (except of course the receiver) under the current parts availability and pricing, the asking price is about average. It is not a smoking deal.
The question is, in your own words, what makes it a National Match? I shoot a lot of competitions with my match conditioned M1As, a couple double lugged and single lugged all in McM stocks and heavy barrels. I never paid attention to the SAI nomenclature. Not to be smart xxs I can stamp NM on any barrel with the best of them.. To be clear, what kind of rear sight does it have? Is it the NM 2A with hood or is it the standard sight with ball and detent? How about the front sight, standard or the 0.062 post? Is the handguard glued/epoxied to the front band? Is the gas system unitized? Is the stock bedded? What kind of stock is it? Is the receiver lugged, most likely not? What are the visible USGI parts, bolt, trigger group?
The reason I am asking these questions, a friend was so proud he picked up a "NM" M1a. Upon inspection the only NM in the rifle is the barrel was stamped NM and it is a standard weight skinny barrel. The rear sight is standard 1x1 click and loose as a goose, non unitized gas system, not bedded, and the trigger pull has a mile long creep. Oh, it has a NM stamped front sight, forgot that one.
Just trying to help.
Nez Rongero