Generally, a square or retangle box for a 10" should be no more than $125. If you wanted a single angle on that box, it would be another $50. 12" boxes are $150 for rectangle or square. Add another $50 for 1 angle. 15" depends on the speaker itself. If its very heavy, the inside of the box has to be braced or the woofer can blow it apart.
Subzero makes some good boxes. If I were forced to buy a pre-fabricated box, I would get some silicone sealant and run it between the pieces of wood inside.
Their website is:
www.subzeromfg.com