Thats a bandpass box, they suck for certain apllications (liek COntour's.)
Your standard 2 port dual sub enlosuyre box will be the best bet for you.
HOly crap they rape you on Box prices.
Have any woodworking skills?

That 90.00 Q-logic could be made wiht 1 piece of 1/4" MDF, 1/2 yard of fabric, adn 1 tube of caulf.. oh, and the box building kit from cruthfield for about 30.00 total.