Plywood attached to rafters to vent the soffit.

I'm looking to add insulation to my attic. It most places the insulation is only about 6 inches deep. There are soffit vents but now baffles. With the small amount of insulation blocking the vents is not an issue, but I want to add some before I add the insulation. I saw at the big boxes they have the baffles for around $2 per. In the attic is an abundance of 1/4 ply 2x8. My question is: Instead of using the baffles can I attach the plywood to the underside of the rafters. I counted about 70 gaps so $140 just for the baffles vs. using free plywood.