Its hard to say if that's too much or not without seeing and inspecting gun. I bought a 66-3 2.5" early this year for $539 that was mechanically tight and sound, but had some holster wear from being carried by farmer. It was hardly ever fire, but no box or papers and rubber grips.
I know a -3 is not as desirable or valuable as a -1, but for $750 I'd want excellent condition, S&W wood grips and no rust. If you haven't bought yet, be patient and look often. You can get some great deals on Gunbroker with some patience.
The bottom is; if you're happy, that's all that really matters.