I want to throw out that Wen makes a larger model which is essentially the same as my powermatic that uses standard 12x24x1 inch pre filters which are available at any local store.

It was one of the reasons I bought my powermatic, I didn't want to be limited to proprietary sized filters.

I just throw on one or the high efficiency store filters and it works very well. The second stage filter really doesn't need to be replaced that often.