I bought a new 4" stainless a few months ago for $400, which was the best price you could get around here at the time. I have noticed since that local prices are creeping up to $410 to $425.
Based on that, $300 for a gun in nice condition is probably not too bad.
I say if you want it, buy it, and don't look back on the price. It's likely going to last forever anyway. In a few years, the $300 will sound like a pittance.