Nahh, don't buy any of those Aluminum filters, etc. The cheapest, and easier way is to get some household airvent filters from your hardware store.
Mine came just about the right size for ALL OF the 3 80MM fans!!! I only had to trim off abit to make the length right. Then take off the lower front plastic bezel. YOu should see lower 2 fan slots, and the HD cage. All covereed behind that metal casing. And you put the filter between the metal chassis and front bezel. I just tied 2 pieces of metal wires thru the top 2 corners of the filter and let it hang there. It coveres all 3 fan slots. THen I put back the bezel, and walahhh! All 3 fans are filtered.
This is very nice, and filteres REALLY WELL! Because these filters are designed to trap all household dusts, works better than those metal ones. One caution, use some medium to high CFM fans for them, because the filter cuts down airflow somewhat. I have 3 intake and 2 exhaust, balances quite nicely. This is very nice, and cheap to do too. When I need to dust the filter, just take off the bezel, and dust.
If you have any questions how to do this, just ask.