I think the Rugers and the Sigma are a bit large for concealed carry. The Sigma also isn't a highly regraded model. $400...maybe rather than compromising and buying a cheap model, save a bit more and buy a better model. If this is to be a gun to carry and possibly defend one's life with, why compromise on quality?
In keeping within a reasonable price range and have it beinga quality make/model, I'd suggest a CZ 2075 Rami.