Price IS an object.

You want the gun to do more than double duty.

I'd suggest you buy a gun you can afford that is suitable for ALL of your intended uses, and then find the buckshot load that works best out of it.

I'd consider mounting a scope and using that to point your buckshot as accurately as possible. Lots of guys are shooting turkey guns with scopes. Then find the choke tube/buckshot load that gives the best results. I don't know if there are barrels manufactured with rifled sights that also take choke tubes, but that could also be a good way to go rather than just a bead front sight.

I'd recommend that buckshot be used out to say 50-60 yards. You may/may not get a tight pattern beyond that range, but to me the buckshot doesn't carry enough whallop.