I would recommend a used Remington WINGMASTER 12 gauge pump. These are arguably the best pump guns out there.
Now, one might argue that if you find an Ithaca Model 37 from the right years, that's more elite and might fit you better and bottom ejection is better for lefties and finding your spent shells after you shoot.
Another fella might argue that an older Mossberg 500 is cheaper and just as reliable, even though it might rattle a bit, rust maybe more and that safety is strange.
New? Well, they are going to rattle a bit more and will probably work fine with a stiffer trigger and plastic stock, the screw-un chokes might not be that great and unlike a nice used gun, the new gun will lose value the instant you pay for it if you end up wanting something else mid-season.
Budget over and under? This is like buying a cheap used car. If you know how to work on them yourself, these can be very good deals. If you get lucky, they are great deals. If you don't get lucky, you're going to hate the day you "saved" a couple thousand dollars, because you're sick and tired of sending your shotgun back for service. You want to go hunting, not to the UPS station.
Oddly, semi-automatics are now perhaps the best value choice. Once you take both kinds apart, you'll see why- the semi-auto has many fewer parts.
I would not turn up my nose at a Mossberg SA-20 or even the 12 gauge, or the very similar Tristar Viper G2. Budget guns, they will benefit greatly from a deep clean after purchase to get the packing grease out of the guts, honing the action by cycling it by hand (or shooting lots, but it seems wasteful to me to cycle the action by using shotgun shells when elbow grease is free.) And then, you probably really want to spend another $70 on a trigger job, or the $20 spring kit from Wolf.. and knowing how to lubricate stuff.
Don't worry about screw-in chokes, in my opinion, Modified will do it all.
My Full choke pump gun patterns about the same as my modern 5/10 choked Fabarms, but it's well known that those fabarm chokes are tight, and more like IM... the bottom line is that no matter how the shot presents itself, half the time you'll have the wrong choke in anyhow. Don't worry, the difference between Mod, IM and FULL in a shotgun really comes down to individual guns and the pattern board, even for brand new guns. They all work fine.
As I said, there is real value in a used fixed-choke pump gun. Everyone thinks that not having screw-in chokes is a deal breaker. It's not. Anything from MOD to FULL will work great, and your knowlege now saves you $100 or more.