Messy Butt

I would stay away from chemically treated wipes. Read the ingredients
to be sure. I just donate a couple of washcloths to the cause (one in
use, one being cleaned) and keep a damp one handy in a ziplock bag.
It's a lot cheaper than papertowelling in the long run, but that works,
too.

Call the local groomers in your area. Some of them will do cats.
Usually cheaper than the vet. Be sure they do other cats, though,
since your cat is not pleased with grooming treatments and will need
restraints. The vet will put your cat under to groom him. Easier on
the vet, harder on the cat because anytime you anesthetize an animal,
there could be complications. This is why it is more expensive.

One thing you could do to help the groomer is add a calming homeopathic
preparation to your cat's water for a couple of days before the
grooming appointment. It may help.