There were a substantial number of Greek '03A3 returns to this country several years ago. Does this rifle have import marking? If it originated from CMP it well not have import marks, CMP is exempt from marking imports.
The prices of '03A3's keeps going up and up, $600 for a nice looking rifle with all R marked parts does not sound out of line. Three or four years ago it would have been a high price, but not today.
The green in the bore is cooper and should clean up with some #9 or other bore cleaner.
The CMP forum is a great source for M1903 info.