Firm Feel charges $450 to fully reinforce a K frame, and that includes hot tanking, blasting, and checking to make sure it's straight. And it doesn't take all that long to weld one up, especially if you've done it before.
You won't get your hands on a Miller, Lincoln or Hobart MIG welder with a gas set up for less than that. Sorry, you just won't. The flux core set ups from those brands that max out at 1/8" thick steel are $300+, and you'd still need a helmet, supplies and some training or at least a bunch of practice, so, more supplies. And you'd still have a flux core set up.
I'm all for buying welders, taking classes, and learning to do it yourself. But be realistic. You won't do that for less than Firm Feel charges to reinforce a K frame. Even if you bought a harbor freight welder, added a gas set up and bought the supplies you'd need you'd have more into it than $450. It costs $80 to fill the cylinder for my MIG, and that's an exchange.
Like I said, I'm all for doing it yourself. I do. But if the K frame is all you're going to weld, you'e not going to save money learning to do it yourself. Not if you're in driving distance of Firm Feel. Now, if you have a bunch of welding to do, it's a different story. But the initial buy in is still going to be more than $450, it's the long run where you might come out ahead.