I bought three sheets of plywood for just under $30. Add a box of screws and it put me right at $30. I was able to get a 22x34x60 bloom box out of it and with the remaining pieces I was able to construct a veg area able to hold 3 moms. A buddy hooked me up with some mylar so I was able to avoid that cost.
so in reality i wouldn't have been able to build anything nearly as good for the same price...
factor in painting the walls white, and the fact that my tent is 6ft tall, lightproof and is easy to disassemble and fit into a small space when not assembled and you're really comparing apples with oranges.
There's a reason there's a market for grow tents and not just grow boxes.