Budget is always a problem and finding a balance between that and safety is tricky. A box fan and filter needs to be set near a wall so it creates a circulation. In a two car garage, I'd set up two fans on opposite walls, suspended from the ceiling With an attached garage, the problem will be tracking sawdust into the house, and having the fine, suspended particulates leak into the house.
Sawdust extraction at the tool is also very important. Sweeping up sawdust after you finish working is likely to only launch more fine particulates into the air. I spent a lot of money trying to put together a good home brew DC (Dust collection) setup, none of which really did the job. Finally, I got the Harbor Freight unit, on sale now and again, for $187 with a holiday weekend 25% off coupon and on sale. Still had to buy a couple of other parts and a 4 inch hose to attach to different tools. It cost me about half what I'd spent on various parts, blowers, barrels and such. I have two, one in my 12x24 shop that has a really fine additional drum type filter, and the other in my garage where I prep wood and resaw. The garage unit just has the cloth filter. The shop's canister filter lets me recirculate shop air rather than blow it out along with the heat and AC air.
A good DC system does not negate the need for a mask, eye and hearing protection. The DC units also serve to vacuum up the shop floor and shelves.
All that seems like overkill to some, but for a grand total of about $350, you can avoid a raft of breathing problems. I am a throat cancer survivor and the carcinogens in sawdust are NOT going into my throat and lungs! Discuss this with your spouse so she's on your side on budgeting for this. After taking me through radiation and chemo, my wife had no problem with my investing in good DC.