Do you know exactly what exhaust system your parents dropped that money on? Is it a Dayton blower or similar? If so, that's perfect, and you can check OG for examples of how to make your own carbon filter, some even work specifically with dayton blowers... here's a link..
http://www.overgrow.com/growfaq/t151
check out the carbonfilters and carbonscrubber faqs... peace..
As for your grow area, yes you'll want to get it as clean and sterile as possible.... Or you could always get a large cabinet/cabinets to grow in... Might be a little easier, allow perp harvests easier... and save some work... just something to think about...