If you don't like the fumes when using a hot knife, but still want a tool that cuts foam like butter, oscillating multi tools works great and are very inexpensive. $14.99 with coupon.
https://www.harborfreight.com/...E1NDgifQ%3D%3D%0D%0A
They also sell an inexpensive hot knife if your cutting outside or in a well ventilated area.
https://www.harborfreight.com/...hot-knife-61423.html