I havent found any new 1911s for under $700, let alone $550. I know you can get used ones around that price. I personally would not get the Taurus. If your're going to get a 1911 and upgrade it then Id stick with a Springfield. Its one of the cheaper 1911s (compared to the Kimber, Para Ordinance, Les Bahr), and its excellent quality. You can do anything to it. The Beretta 92 is a great gun. I used it all throughout my military career and never once had a problem with it. Im actually looking at buy a 92 to add to my collection now.
Why wouldn't you get the Taurus? I'm curious, as it's one of the 1911's I'm considering buying.
There are several below $700. Para GI models sell for around $600-$650 brand new at shows. RIAs sell for less than $500, sometimes $400, brand new. The Taurus 1911 is $600. Remington 1911's at the last Fort Wayne gun show were $500-$600. There are a couple of other cheaper brands that sell new 1911's in the $400-$500 range as well.