I am looking to pick up a quality used 20ga
Benelli semi auto, Beretta O/U, possibly a BPS pump. More concerned with functionality than appearance, this will be used in the field.
have cash and all sorts of trades
I'm not selling any of my shotguns at present, but I urge you to strongly bias toward a 68x model Beretta OU.
You don't say exactly what type of field activity you are going to use it for so, in 20 ga, I'm assuming this is for upland bird.
If so, I HATE...FUCKING HATE...semi-autos in a field situation like quail hunting. I don't trust safeties or people who "think" their safety is on while with an good OU, you just walk with the action open. Shells in chambers...but action open until dogs are on point and you are in position for the flush. With an open OU, everybody can tell at a glance that the gun is safe.
Also, it kills me when I see 12 ga hulls on the ground at a beautiful GA quail preserve. First, WTF shoots a little quail with a 12 ga and I know these hulls on the ground are from semi's.
I have some very high end competition skeet guns but I have also owned 68x Berettas for a very long time and they are the Timex watch of OUs. Not terribly expensive (well, sort of) and they are REALLY hard to break. They just keep on ticking.
Now personally, I like a 20 ga barrel on a 12 ga large frame gun for the weight....straight 20 ga seem a bit light to me but almost everyone else values that for a field gun. I have a Beretta 682 Gold, two barrel set and I use the 12 ga barrel for SC and five stand and shoot the hell out of quail with the 20 ga. Bought it used and, as I said, it just keeps on ticking and seems to thrive on abuse.
Good luck and my suggestion is, if you can, take your time and keep looking for a good used OU. If you can be patient, you may well find the gun of your keen desires.
P.S. - also, if for upland hunting, strongly consider a wood stock as you can get an adjustable comb kit installed and get it to fit. You are probably already aware that relationship of the on eye to the rib is key for a shotgun and I don't know who the hell standard factory drop at comb fits....but its not me. haha
Cheers