Pretty simple, but messy (potentially VERY MESSY). Cabon dust goes through these cheap filters.
2 filters / 1/2 gallon of carbon / 2 more filters, duct tape.
Approximate Cost: $16
4 filters, $3, Wal Mart
carbon, 1/2 gal, $12 Pet Smart
duct tape, $1, Wal Mart
fan, already there. just added...