Yes, it really exists:
From the article:
"What is Rattlesnake Vaccine?
Crotalus Atrox Toxiod is made using Western Diamondback rattlesnake venom. After vaccination a dog
produces antibodies that will begin neutralizing rattlesnake venom immediately if the dog is bit. Antibody
levels in a recently vaccinated dog are comparable to up to three vials of antivenin. Antivenin costs $500
per vial and is in increasingly short supply. The vaccine costs from $18 to $25 per shot. For dogs under
100 pounds, two initial shots one month apart and an annual booster a month before rattlesnake season
begins are required—a third initial shot is given to larger dogs.
The Hollister Veterinary Clinic estimates that treatment of a vaccinated dog that has been bit by a
rattlesnake will be around $400. Treatment of an unvaccinated dog that is bit by a rattlesnake will cost
$1500 to $2000 or more depending on how many vials of antivenin are required. More importantly to
many dog lovers, a vaccinated dog will experience less pain and will be at less risk of permanent injury.
Typical treatment for rattlesnake bite
Dogs that have not been vaccinated are given from
one to several vials of antivenin, plus steroid
shots to reduce swelling, and antibiotics to
Dogs that have been vaccinated are treated with
steroid shots and antibiotics only—and in some
cases, antibiotics only."