You can find them on line for as little as $75 for a 4x4x6 and $110 for a 5x5x5'6 and $180 with shipping for a 4x8x6'2, or you can dish out the cash for a name brand.
None of the commercial brands work, the best they can do is slow them down and help them to build a stronger immunity to produces.
I ended up dealing with an under the counter treatment they call Doominator, and I doubt it's the real name, but it worked the first application and only had them...