There are several good choices for a range/home defense pistol under four C-notes. The Ruger would be ok, and most of them will have drift-adjustable rear sights. I'm not a big fan of the P-series, as the absolute worst auto I've ever used was a .45 version. Also look at the S&W Sigma, which although has a reputation for a heavy trigger, is actually a reliable and accurate handgun.
I would probably go for a Stoeger Cougar, which can be found at about $359-$379. If I couldn't find one of those, then I would next look at the poly Steyr from CDNN if they are still under $400. If that didn't work out, then the 3rd one I would consider is the Taurus 24/7.