To the OP:
1) The conditions vary greatly, as with virtually every make and model of used firearms. You're area and subsequent used gun market will dictate what's available.
2) Most of the "numbered" smiths will handle +p with ease. Double check with S&W if you have doubts/concerns.
3) I was lucky enough to buy a RB Model 10-5 snub for $330 OTD in great condition back in August of 2011. Area and market will factor into the price as well.
4) The snub Model 10 stacks up very well compared to newer revolvers. My mother ended up taking home my Model 10-5 and prefers it to the SW 315NG that is my current CCW. While I miss the great trigger and heft of the 10-5 (for hotter handloads), for EDC the Big Dot sight. U-notch rear sight, and light weight better suit me for a daily belt gun. Matter of taste, I suppose.
Regards,
Lucky