You can get a small air compressor at harbor freight for about thirty bucks, which would allow you to dust the system on a regular basis (it should go without saying that this should be done outside, not in the room where it will be running, or it will all end up right back in there) which is about the price of a few cans of air. By the time you buy four or five cans of air, you could have a small compressor, and never need to buy canned air again.
Or buy a ten dollar air tank, fill it at the gas station for a dollar or at a friends house that has a compressor for free, and get several cleanings from one filling. Something to think about anyhow especially if you have lots of issues with dust buildup.