I hear ya man.. Cost is always an issue.. I waited a long time for the deal on the 18's.. And I'm still waiting on the amp.. But with the ib, I can add to it, be it more power or more speakers.. It's modular ! And anyone can build the manifold or baffle board.. It's sooooo easy..
Oh yeah, attach a grill, and it looks like a wall vent.. Check out the IB web site for all the details.. Lots of pics of all the set ups, etc.. http://ibsubwoofers.proboards51.com/index.cgi

LFE ! The rest is just details..