My box method using 3/8" plywood and 2x4's cost probably $150 for a 16 miner space. Add my 6400cfm of fans to keep air pulled through at a good click and they are also staying nice and cool with redundancy for about 290watts of fan power. Once I clean the miners out (from where they got dirty before being put in the box) I don't think I will have to do that again for a long time. The fans were $220 for the pair with another $60 or so for the louvers to keep rain, bugs, etc... out. But my wiring and fans were needed simply to run my miners in my space - so I only consider the cost of the box and filters. The filters were the cheapest I could get per square inch of filter - for air conditioning filters anyway.
Building it this way also pulls the air across the miners very efficiently and I'm sure is allowing the bigger vent fans to lower the power needed to run the miner fans. Right now with 10 miners - they should be moving 10 x 250cfm = 2500cfm. The 6400cfm fans are being reduced as they are pulling throught the filters and miners - but even if they are only being half effective, that's still 3200cfm being pulled across the miners very directly vs the 2500cfm they would be doing on their own.
So I would say my overall wattage is probably nearly the same net wattage as if I weren't even running the vent fans. Cooler miners, cleaner miners - Relatively low cost. I'm happy.
Here's pics: