Like the title says I want to add some kind of filter so that the k40 doesnt need to be by a window. My plan is to do craftshows and events like that where I won’t always have access to a window. I know either Epilog or Glowforge(I forget which) has an add on that does just this but its close to $1000 but I haven’t been able to find a lot of other references to something like this. Any advice on filters to buy or even a set up out there that i may have already missed?
FYI and not actually addressing your question, but as a side note for additional information: LionsForge CraftLaser does this too, as a fully self-contained unit including filtering and cooling. $5K total. They charge $150 or $290 (two choices) for replacement HEPA filters alone. I didn’t see any reference to an activated charcoal filter as you’d want for a lot of cutting options. Didn’t see anything on their site about what they are doing for flame arresting. I wouldn’t want to send flaming debris into a typical HEPA filter! 
I you search “diy laser cutter exhaust filter” you will find a number of builds that people have done. Like these:
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The big downside is that depending on the material you are lazing, you might have to replace the filter often which as stated above can be a couple of hundred dollars.
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Yes, it would certainly depend on what filters you are using. You would definitely want some kind of pre filter to prevent the activated carbon from becoming clogged to fast with particulates. Could be as cheap as a car air filter. Bulk activated carbon would probably be the cheapest option for chemical adsorption of vaporized products. Then you would want a post filter to prevent blowing out carbon dust. You would also need a fan with enough CFM to get adequate air flow through the whole filter.
It’s also technically possible to regenerate activated carbon by heating it up hot enough to have adsorbed impurities desorp. Of course this would require about 500 - 900C to bake everything out. Probably some kind of propane powered furnace. It would also definitely need to be done outside because all those impurities will be venting off.
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