Yea im not wanting to spend .more than. $250. For carbon filter and fan
I`d go with a 200mm or 250mm or 300mm box fan, check ebay you find them cheap, I`d go over 1500cmh, like 2000 or 3000 you get some with twin holes this may be better as you may want to run 2 filers or more
or go with a turbo type fan but the mdf box fans are normally better and quieter
you get brands like Gorilla, tornado and lizard
just so long as the motor is good and it works well new or used don`t matte if its a good fan
I would budget between £40 and £200 for the fan, then a good filter is around £60 to £120, get some insulated ducting too
The box fans can just be mounted to a hole in the wall and piped upto the filter or you can pipe them out up to you