I'm sorry that your pup is feeling poorly, however I would not use the Benzonatate.
These are two completely different drugs, and benzonatate isn't used in veterinary medicine.
I understand the cost of treating your dog is expensive, and in today's economy everyone is feeling the pinch, however there are a couple options you can try:
1. Ask your vet to call in a prescription for the meds to someplace like PetMeds.com. These are cheaper than getting them from your regular vet. The only downside is that you may have to wait a bit as shipping is sometimes less than speedy.
2. There are organizations which can help defray the cost of treating your dog, my suggestion would be to contact them to see if anyone can help.
American Animal Hospital Association http://www.aahahelpingpets.org/home " Through the AAHA Helping Pets Fund, veterinary care is possible for sick or injured pets even if they have been abandoned or if their owner is experiencing financial hardship." Angels 4 Animals http://www.angels4animals.org/ "Our services range from financial aid to complete treatment to those pets and pet owners in need." Care Credit http://www.carecredit.com/ A credit card company for health care, including veterinary care. "With a comprehensive range of plan options, for treatment or procedure fees from $1 to over $25,000, we offer a plan and a low monthly payment to fit comfortably into almost every budget." Feline Veterinary Emergency Assistance (FVEAP) http://www.fveap.org/sys-tmpl/door/ "Seniors, People with disabilities, People who have lost their job, Good Samaritans who rescue a cat or kitten - any of these folks may need financial assistance to save a beloved companion." The Feline Veterinary Emergency Assistance Prog ram is a nonprofit 501 (c)(3) organization that provides financial assistance to cat and kitten guardians who are unable to afford veterinary services to save their companions when life-threatening illness or injury strikes. God's Creatures Ministry http://www.all-creatures.org/gcm/help-cf.html "This fund helps pay for veterinarian bills for those who need help." Help-A-Pet http://www.help-a-pet.org/home.html "Our efforts focus on serving the elderly, the disabled, and the working poor." IMOM http://www.imom.org/ "We are dedicated to insure that no companion animal has to be euthanized simply because their caretaker is financially challenged." The Pet Fund http://thepetfund.com/ "The Pet Fund is a registered 501(c)3 nonprofit association that provides financial assistance to owners of domestic animals who need urgent veterinary care." United Animal Nations http://www.uan.org/lifeline/index.html "The m ission of LifeLine is to help homeless or recently rescued animals suffering from life-threatening conditions that require specific and immediate emergency veterinary care. We strive to serve Good Samaritans and rescue groups who take in sick or injured animals. In certain cases, LifeLine can also assist senior citizens and low-income families pay for immediate emergency veterinary care."
Good luck and I hope this helps!!