You can probably find a 4" GP100 for less than $550. if you shop around a bit.
I own both S&W's and Rugers. Both are excellent revolvers. Rugers are built like a tank and virtually indestructable. S&W's are somewhat smoother and generally lighter. Both have their good and bad points.
If you want a good HD handgun, you'd be hard pressed to find something better than a 4" GP100. It's stout and will handle any round you feed it.
Just my 2 cents.
“If ye love wealth better than liberty, the tranquility of servitude better than the animating contest of freedom, go home from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains set lightly upon you, and may posterity forget that ye were our countrymen.” ― Samuel Adams