... but canister-size carbon filters will run you 99bux and up in my 'hood, and though they save ya the muss'n'fuss, there are some good threads around here on DIY carbon filtration, with pricetag somewhere in the 40bux range.

As far as finding inexpensive 12v adapters to power fans, as well as the fans themselves, if you live in any major centre, there should be an electronics surplus house in town somewhere; the place that gets the remainders of everyone else's junk, but a great place to scout bargains. I found a 2A 120vAC in, 12v out adapter at the one on Queen St. for like 10bux. Way cheaper than the 1.5A one at WM for $15

You can string a /lotta/ compumuffinfans on one o' those...