STI frames for their all steel guns (Trojan, Ranger, etc.) are cast, that's why they are cheaper.
STI frames for their double stack guns are machined from bar stock, and grips of course are injection molded.
If you want to be competitive in limited class, you are talking 1911 guns (whichever you can afford), or Glocks. Glock 35 works great, or now that they lowered the power factor Glock 22 is an option.
Limited 10 brings single stack 1911s in the arena. And Steyr M series in .40S&W would be a great alternative considering how cheap they are these days.