Seeking subwoofer recommendation

I am looking for advice on a subwoofer to pair with Vandersteen 2CE speakers and a Rogue Cronus Magnum II integrated amp. It is my first foray into sub-ville, and I want a decent sub (new or used) for less than $500. I know there aren't stellar performers at this price-point - I just want to dip my toes in the water and see how the sub sound contributes to my system. Feel free to recommend subs up to $1000 if they are a much more worthy performer. I want something that will integrate well. Thanks in advance for any recommendations.
Room size is 18'x15' with brick walls, wood beam ceiling and fully rugged.