Sarco has Rock Island pre-fit frame kits on order, supposedly coming in November. These are (I've heard) the same frames that STI builds off of. They cost about $200 for frame, slide, barrel, ejector, and mag catch.
Essex also sells frame/slide combos, for about $250-300. Keep in mind you're going to have to fit a barrel to them. Caspian frame/slide combos are that price or a little more. Once you get into fitting frame/slide/barrel/bushing, the 1911 becomes a work of art as opposed to a firearm. That's why I went pre-fit or drop-in for all the parts on my first build. Took me 7 hours total to build, and I made a lot of mistakes, but it turned out in the end.
I put Brown and Wilson parts in mine, at least for the parts that needed to be high quality. Grip screws and stuff like that I went with whatever was cheapest. Sights are some very tall LPA adjustable target types. Scarily accurate, but I'm still not sure my staking on the front sight is going to hold up, even after 100 rounds. Time will tell, but it'll be an easy replacement if it flies out.
For $750 I got a pistol with options that I'd have to pay $1500 for, and it's run without a hitch for the past 250 rounds. It's not the prettiest gun, but it doesn't have to be. It just has to work, and it does.
Building a 1911 is lots of fun, and a great learning experience. Take the "easy" way the first time and learn the weapon, and then do one with more custom fit parts. Good luck!