Used Winchester pumps can be had for $200-$400.
Used Mossberg 500s can be had for $125-$300
Don't overlook double barrel guns, they have some benefits over pumps. Quick loading and unloading, and quick fire. Lighter and more reliable too. Only downfall is only having 2 shots. If you are on a tight budget, used H&R single shots can be had for as little as $35.