In my opinion the K-Frame is too small and slender for the .357 magnum.
The model 19 was created for police use. At the time, it was the smallest, lightest .357 magnum available. The lighter size and weight, compared to the N frame made it a big hit with people who carried a revolver several hours a day, day in day out, and didn't shoot it much.
Meant to be shot mainly with .38 Special, and occasionally with .357 Magnum, it was proof of the concept that Bill Jordan and other influential gun writers and policemen had been lobbying for.
Its a great gun. I had one for several years a 6" P&R, although I now forget the -number. I have a no-dash model 66 I inherited. Also a great gun.
They do, however, have their limitations, and they are NOT model 28s or 27s!
They cannot handle the heaviest loads, loads in the original .357 Magnum levels. The 28 does.
My opinion is the quality of the pinned & recessed guns (either model) is the best S&W ever did. It is damn good. When you get to the newer models, the quality sometimes suffers a bit. Few will argue that the newer guns are fully the equal of the older ones. Some are still VERY GOOD, just not quite as good, to my jaded eye.
As to the price difference, I would eat it and shut up. Its a one time thing, right? Model 28s are now going over $700-750 at gun shows in my area, WHEN you can find them. One friend of mine recently scored a "deal" on a pre-model 28 Highway Patrolman for $900! Gun is about 95% still has the original grips (#'d to the gun), a very sweet piece.
Bottom line, if you are fully satisfied with what the model 19 gives you, the 28's extra weight and strength aren't needed, or useful.
But, if you want or need what the 28 has, and is, NO model 19 can give it to you.
Your call.