OP- personally, I would look for an older MKII. Well built, all steel guns. I have found them new-in-box recently for ~$300. I am not a big fan of the MKIII because of the mag safety and the price of the all steel models. The MKIV doesn't interest me at all because I have so many MKIIs already. The take-down feature is nice but once you figure out how to do it the right way, the MKII is a breeze. Download the instruction sheet of the PAC-LITE upper for a super easy method for reassembly that works right the first time, everytime.
Alternatively, you might consider a Ruger SR22. I have two (one is a suppressor host) and they both run flawlessly but they can feel a little small in the hand and have the mag safety and counter intuitive thumb safety/decocker.
Ruger Single-Six is always a fun choice.
Avoid the Sig Mosquito. Ask me how I know