currently building CPU Case. would like to have a washable inlet filter an screen aproxx 10" X 4" that would keep dirt out of the case
More aboutcomputer vent filters
I know this will sound awkward but this is a viable option that is essentially very cheap and easily cleanable or if you want just replace it. Try using cooking hood filters, you can cut it out and mount it in the part of the case you need it to go. May look ugly if it outside or doesn't match the colour scheme. Just for the record, that was not my idea, it was Brett928S2's idea. Read the link below if you want to read the thread where he made the idea.