HK USP Compact, HK P2000 & P2000 compact, HK P7 series, Glock 19 or any of the smaller Glocks (don’t know the model #s), SIG single stacks, a reputable shop’s 1911s, Walther P99 & P99 compact, Springfield XD & XD compact, and on and on and on. These are good quality guns to look at as a start. You might be able to get a used USPc for $400, but it's doubtful. Glocks are around $400-$450 new. Sigs are around $400 used.
I’m in the USP Compact boat at the moment myself for what it’s worth.