Exhausting out window at half speed
I'd say ~$400-450. I purchased the insulated 8" air ducting and vents from Lowe's and everything else from Amazon.
Fans: https://www.amazon.com/gp/product/B01CTM0LLO
I would make your own air purifier. https://www.amazon.com/VIVOSUN-Inline-Ventilation-Variable-Controller/dp/B01CTM0LLO
get something like this, buy 4 HEPA air filters that are on sale from whatever big box tool store. use metal duct (the stuff for vents) to tape it together. use the styrofoam from the packaging. also, since its 4 sided and a cube is 6, put duct tape at the bottom of it to seal it.