Can anyone recommend a low-cost filter face mask suitable for spraying synthetic enamels? I'd like something that has replaceable inserts, because it's going to take me a few years to finish building my engine and so it'll take me a few years from start to finish of the painting. I was thinking that a non-replaceable mask might life expire, whereas a replaceable one I could just buy new filters for before a major painting session. Or should I stick with the fixed units? Have looked at 3M 4000 series masks.