There are a heap of subs out there in the ~$400 category. Alpine, ID, Focal DD, JL, Treo, RF all have offerings in your bracket. I find your lack of power disturbing, I don't know whether 150@4ohms or 300@2 will satisfy your wants with Dance and RnB, it'll get the sub moving for a while though.
QUOTE
[apparently the challenge is also refreshing a thread before I post...Damn you again Shiny Jnr!]
You were almost 20 mins late to the thread

I can't help that now can I

Edit - Do you plan on making your own subbox? In
this thread of yours you're chasing a prefab one, but if you create your own I'm sure you will have a lot better results.