There is a product called Ona gel that I once used. It comes in tubs and even tubs with fans attached. When I built my first CFL cupboard which was a chest of draws with the guts of the draws taken out I used the Ona gel in that. Now I ended up changing to hps for flower and had a real crap system so I cant speak for it as far as when I flowered.
However I also built my mate a bigger cupboard which was a wardrobe layed down on its side. He used it from seed to harvest. He used the same Ona gel I did. Now it didn't remove all the smell, there was still a bit but it did help a lot. The smell was just in the room he used and I never noticed it anywhere else.
There are a few DIY carbon scrubber systems available, probably on here if you search, if not google them. You could run that inside without cutting holes and just clean the air. I have not used one so cannot speak for there effectiveness in full flower!
I'm not sure whats available as far as pre made fans and filters for you but the cost of running them is not large at all.
If your not venting out though will you not have temp problems? Sorry I don't know how big your area is!
Ive just dug out my 4" ruck which was packed away. That runs at 60w and 70w depending on wether you wire it at low or high power. the DIY things would be a hell of a lot less. From that you can work out the cost.
I think you could pick up a second hand fan for real cheap, you could buy a second hand filter but obviously that could be past its useful time unless it states only used for a week or something. As I said if you've got the space you don't have to cut hole for extraction. There is the issue of air exchange though and heat removal!!
Good luck either way.
C.W
