You might be able to build some nice speakers using the excellent HiVi SP10 drivers on the site as subs. The smaller size will reduce the overall cost, but even then I bet it's $1000/pair.
I looked into this, but then I found a trashed pair of Klipsch Heresy Industrial speakers and restored those. In truth, finding a solid pair of cabinets might be a nice way to go. Something like old Peavey cabinets are extremely well-built, and you can even peel the nasty carpet off them and repaint them with something like Duratex.