If it's a 357 magnum with a J serial number I think he has a one of a kind.
In gKitch's excellent condition, I would say the value is close to double his posted range. Depends on how 'excellent'. My opinion only.
Ed
Assuming it is wearing S&W factory grips and is in excellent condition but has no box, fair money would be somewhere between $450 and $550. There are some S&W lovers on this forum who will say $more, and any gunshop will offer less, but that is a realistic street price. If it is wearing aftermarket grips deduct $50-$100.
Barrel length has a HUGE effect on value with the 357s. Everybody, his brother, his preacher and his cousin Ira wants the 3.5" guns. The 5" models also have a strong following. The 6" guns fall dramatically in demand the therefore price. The 8" guns fall even further.
Some are snorting at $500 +/- for a nice 357 but if it has the long barrel this is not a ridiculous appraisal. Sure, sellers will ask for a grand or more, but how many actually sell?