How much do you want to spend and what do you plan on doing with it? Do you want a repeater, or would a single shot be good? Do want it to just shoot slugs or be more versatile?
The savage bolt actions are really nice for the money. The H&R ultra slug guns are very hard to beat for the money. The down side is they are a single shot and on the heavy side. I own one of these myself. Other than that a mossberg 500 or remington 870 with a good cantilever scope mount slug barrel are pretty decent, and you can do more with them if you want. If you want a semi auto the same thing can be done with an 1100 or 11-87.
These are probably the most popular choices you will see. Used I think Marlin and mossberg both had some bolt action slug guns at one time. I couldn't say what the prices would be.
You could also go with a browning BPS, but it will be more expensive than the mossberg or remington. It is a nicer gun though, and the barrels have a faster twist rate and should work a bit better with the newer faster slugs on the market.
Once you get away from these you are talking thousands of dollars or close to it. A browning A-bolt slug gun would be great if you could find one, and afford it. And the tar-hunts are nice, but pretty pricey for a slug gun.
Just depends on what you are looking for. I have seen the remington combo models shoot 2 inch groups or so at 100 yards with a good scope, good shooter and ammo they like. My H&R ultra is not much better than that, just handles recoil better because it weighs a ton and a half

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Oh, I forgot Ithaca deer slayers, I don't know what they run for price now though. They are a pump action dedicated slug gun.
Paul