Hi Jingle, not a problem bro, i am in the same position as yourself and i have finnished my grow room for under £20, get a piece of 4 inch pipe, buy two small boxes of activated carbon and get a pair of ladys tights and one roll of duct tape, when you have all the components let me know and i will show you how to make it, you can buy the act carbon at any pet shop, it is sold for fish tanks.
If you go yo your local dump and tell one of the guys there that you are looking for a 4 inch fan, they will have one for you in no time or just ask to look through the electric part of the dump, you will get fans from pc box, hoovers, kids air hockey tables, i have built my grow room from the dump from pots to mesh from fans to pipes, so you must use your imagination to solve these problems and i will help you aswell, so relax and start getting the components that we have talked about and let me know when you are ready and i will go through the process of building the carbon filter with you, by the way i smoked a loaded bone and blew all the smoke into the box. it was extracted and i had my nose at the other end after it came through the filter there was no smell at all as i doubled the carbon layers, just to make sure, so i think we will do the same with yours my friend, hope iv helped, keep on rocking in the free world, peace and love bro