Well, U could buy a cheap compact GI Model.
But, most of the $500 fullsize ones are still just Mil Spec models. I don't personally count the Charles Daily and RIA guns because I'd never buy one .
But, most of those small ones have bull barrels, and they take more work to fit properly. Many also have the same bells and whistles of the fullsize guns.
Also, those smaller 1911s are more likely to have issues, so I guess in general, more work is put into them...