My closest LGS has new Gen 2s (Glock 22 models) sitting on the counter - unsold - for $399, plus tax.
I suggest that you get what you want at a price that you are comfortable with. Don't worry about just 'getting a bargain'. I might add that you will get a decent warranty with a new Sub2000 and not likely any warranty with a used one.
I have a Gen 1 9mm (Glock 17) and a Gen 2 .40 S&W (Glock 23). Both are modified to make them more useful to me (I do not like either Generation Sub 2000 as initially made). Each has their own strong points and weak points. Most important to me is the Gen 1 barrel nut threads on and the Gen 2 barrel nut, although threaded, is more like forced on over glue. I actually prefer to shoot my Gen 1. It has a much better trigger.
Edit: I have never had a fail to fire or eject with either of mine. That said, I don't have enough confidence in either of them to carry 'on-duty' as a LEO or to be my primary self defense firearm. I have several other guns that cost as much as 3 times more $ that I feel the same way about. I cannot tell you why I feel that way because I honestly don't have any reason to justify feeling that way. My Sub2000s are fun to shoot guns here on the farm and I often have one of them with me just to keep me company and to enjoy engaging 'targets of opportunity'.
Good excuse to post photos...
Gen 2
Gen 2 on left / Gen 1 on right carried on my Arctic Cat
Gen 1 on top / Gen 2 below at my range.
