This is an older post from home depot that I would like to discuss

This is too expensive to put on all the vent pipes on my house, which amounts to 5. $150 to foil the gnawing squirrels. Sheesh.

Yes, 150 dollars to fix your vents may seem like a lot. But call a roofer and see how much that is. Usually its around 100 dollars a vent minimum. So that’s 500 dollars in this case. They will also be pulling shingles which can leave an ugly repair.
You can also go up yourself and put on some screen. But that’s not going to fix the vent. So you can spray in some foam in the gap, but that’s not going to last. By the time you do all this you have spent well over 150 dollars of your time and effort.
Or you can just buy some Critter Quitters, cut them on the ground with a saw, put your screws in, go on the roof and put them on. Takes about an hour and your vents are fixed for years.
Seems pretty inexpensive to me