I put household fiberglass bug screen on the front of my grilles. The nice soft stuff. I attach it under the trim under the hood above the grille, let it fall over the grille and then tuck 6 or so inches of it behind the bumper. It stays put, works, is easy to clean off and if there is any cooling issue, you can rip it off on the side of the road.
Cost $2 or less.
If you trim it nice it looks good, a week of driving and the sun hitting it and it lays very flat and tight.
Only time I had cooling issues was I used some of that super tight screen for 'no see ums' kinda bugs. It's a little tight and did restrict air flow too much when it got above 100F outside, regular screen has been fine.