You can probably get a 1-2 million serial number from the CMP. If you order a service grade your chance of it having an original barrel is very slim. I was at the GarandCollector's Meeting in October and was one of the 250 or so members that sorted through 17,000 Garands. One of the things I was looking for was WWII receivers with original barrels. Better than 90% of the WWII SAs that I handled had been rebarreled with early 1950s barrels. I found one 2.23 million SA with a nice 10-43 barrel and found a nice 1.8 million barreled receiver in the South Store with a 6-43 barrel.
If the 1943 SA for $1,500 is original finish, has a low wear barrel, uncut op rod, and everything is correct and matches up well for finish and wear (except for the stock), I think that is a fair price. WWII rifles in original configuration are getting harder and harder to find. Finding 1945 or 1944 era original receiver / barrel combinations are easier to find. The earlier you go back, the greater chance that the rifle went to war and the barrel was used up and replaced.