The Sig and Beretta are not steel, only the 5906, Browning and and CZ. All but the CZ are good guns though. I've had too many negative CZ experiences to recommend one.
There are tons of police trade in 5906's out there. Around $300-$350 with one mag seems to be the going rate and I'd bet this is one. I'd look it over closely. Most are in rough shape externally from being carried for years, but not shot enough to be worn out. Our local PD just traded in some for Glocks a few months ago. Some of those guns were over 20 years old. Some were rough looking, but in the 20+ years those cops carried the guns they never gave any problems.