Just silicone a baffle to a 5 gallon bucket and poke a hole in the back for a port.
On a serious note though... I am in the process of building my first large ported box (have built multiple sealed) and will see how much of a difference it will make over my previous ported prefabs. I hope it does pretty good, I already have 80 bucks into just the wood (2 sheets of 1" MDF).