1911
I picked up a used SA GI model, which improved iron sights installed by the previous owner, for $400 at a dealer in Boise, ID. If you like 1911s a used SA GI is a great gun for the money. Also search here for the Rock Island Armory (RIA) and Taurus 1911s. Both are available new slightly under (RIA), or over (Taurus) $400. Both have gotten good reviews here. Also see the forums
www.m1911.org for more input. There is nothing that can match the superb trigger of a 1911.
Hi-Powers
If you look around you should be able to find a used Browning HP at or maybe a bit over $400. Fabrique Nationale of Belgium owns Browning, and makes the Hi-Power. FN did import some FN marked Hi-Powers, but they did not sell well in the US where the FN name is lesser known. They were closed out, and with some looking you should be able to find an FN HP new for between $400 and $500. For a gun of that kind of quality it's well worth saving a bit extra to buy. While not a 1911 the Hi-Power does have a pretty good SA trigger (really good with the magazine safety removed
), and their very slim slides make carry like a much smaller gun. They really don't feel like a twin column magazine pistol in the grip either. They're great guns. Also do a search here for the FM (Argentine Copy, formerly licensed by FN), Charles Daly (US assembled from FEG Parts with very nice XS sights), and FEG (Hungarian Clone) Hi-Powers. Those will offer a less expensive alternative to the FN/Browning Hi-Powers.
SIG CPO
A Certfied Pre-Owned (CPO) Sig would get much closer to your budget. If you really want a SIG then it's worth saving up the extra. The CPO guns are certified by SIG and carry a one year faactory warranty if I remember correctly. Everything I've read here indicates that the CPO guns are a great value.
More Ideas
Last, but certainly not least I'll lump together some other pistols that I feel are great options. CZs are well regarded here, and most big box stores sell the CZ-75 for just over $400 new. There are always plenty of steel and alloy frame S&W autos on the used market at well under $400, and those a great guns that are often overlooked. The FN FNP has gotten great reviews here and is also available at just over $400 new.
Take a look at what's out there, see what fits your hand, and what you like. As others have said, if what you really want is a bit more expensive than you planned save up. It's worth the wait to get what you want rather than settling for something else.