I have a very similar Hi Power, made in Belgium during the Nazi occupation. Mine was later factory rebuilt & sold to the Austrian State Police. Since yours is a fixed-sight model, it likely has the WaA 140 mark. It's not clear what the serial number suffix is, but each letter added 100,000 to the S/N range after 200,000. Thus, 60020a would actually be 260020 in sequence, in the range 200,001 to 300,000. The last pistol produced was circa 63000b.
If your pistol indeed is marked WaA 140 (as I think I see) and has wood gips (which it does), it is the most common WWII Hi Power variant, made from late '41 to the liberation in '44. Were it to be marked only with the Eagle over N proof mark, it would be very rare.
I don't see the trigger pin for the magazine safety; since the Germans didn't like the mag safety, it was generally disabled, and, after mid-'43, eliminated completely; thus, the lack of trigger pins in later WWII production triggers.
Your trigger guard has "MR" stamped on the left front. I see this mark in Vanderlinden's The Belgian Browning Pistols on both Wa 103 and WaA140 pistols he illustrates, but Vanderlinden does not define that mark. Not all WWII Hi Powers have it.
The German designation was "Pistole 640b," the "b" for Belgian.
As for value, I really don't know. I'd guess 500-750, but I'm not a Hi Power guy. If you have the original WaA-marked holster, the value would be higher, of course.
A nice find, overall.
Regards,
Walt