Might I suggest you cruise over to the VMPS website and check out their offerings. The Co. has won awards at the CES show in Vegas and has several different subs, one may fit your budget and if you are a DIYer they are available as kits. I'm very pleased with the Larger SUB in my little system.
(passive radiator .. 15" and 12" running in full frequency @ aprox. 150 lbs)
My neighbors love it too,
pc