It looks like you are looking at
this Dayton sub. If you have narrowed it down to just the two listed subs I would pick the Dayton hands down.
Now that the recommendation between those two subs is out of the way I would recommend buying two of
these Dayton subs after shipping it will probably be slightly more than $250, but not much and you will have a far better sound quality than the previously mentioned option. There are a few reasons for this. First you will have more headroom due to the larger moving surface area, but more importantly with proper placement and setup you will have a far more linear response than likely possible with a single sub alone.
I realize that you might not have the room to have two subs, but I just thought I would throw it out there. Either way Dayton is the way to go, but with your budget I would strongly suggest picking up two of the smaller Daytons to get the highest fidelity in your specified price range.