The 1991A1 Colt is a no-frills 1911 or Government model. Colt began producing these pistols ten years ago to compete with basic models by Springfield and a few others. The frame and slide of the 1991A1 are forged. Other parts on the pistol may be cast or plastic. Sights are nothing fancy but work. Out of the box, the pistol operates properly, although it may be not sighted-in correctly.
The pistol is a good base for building a Gov't model to your specs. On mine I had Cylinder and Slide do one of its package upgrades on it. This work includes a new trigger, sear, and spring, slottled hammer, 18.5 # guide rod spring, Novak sights, extractor properly adjusted, internals polished (including the feed ramp), C&S thumb safetly, and a few other minor improvements. I use Wilson 7 round mags (#47) with it. It is a nice carry piece now and suitable for IDPA and other such events.
Price: Expect to pay around $500, maybe a little more. Prices have been going up again lately. Expect to spend from $500 to $2000 on custom upgrades, depending on how enthusiatic you want to get. I advise basic modications for accuracy and reliability, nothing more. Such work usually cost me around $1000. If you can find a used one in good shape, this move could save you a few dollars but still allow you to build a fine pistol. They routinely turn up for sale here at TFL.
Don't believe the negative remarks about the pistol. It is an excellent weapon that gives you room for that personal touch for which firarms enthusiats are known. Gunsmiths who work on the 1911 (for example, Bill Laughridge, Terry Tussey, and the late Brian Bilby) advise their customers the Colt 1991A1 is the one to buy for a decent custom upgrade.
Good luck with the project. I have a second one on its way to Cylinder and Slide soon.