Parvo is serious--it would be best if you could work out something with your vet.
I found this but it sounds complicated to administer:
Effective home remedies
Home remedies for parvo work amazingly and display great results in majority of cases. When you cannot afford veterinary care or treatment for your dog you should employ these home remedies as soon as possible. Remember that a dog does not have a lot of time as the virus is steadily affecting all major systems of its body. After you begin home remedies for parvo maintain a record of everything you do and if you do not see improvement within 6 hours you need to take your dog to the vet immediately. There is a limited amount of time in which you can save your dog; hence you need to act quickly and meticulously.
The very first remedy for parvo is definitely to keep your dog hydrated. Parvo is an infection that causes diarrhea and vomiting, both of which can lead to severe dehydration. A dog may not want to eat or drink but you should force feed water.
To treat diarrhea use Pepto Bismol and administer doses using a syringe. (I suggest you to buy a liquid pepto bismol because it is more easier to administer to your dog)
To cure this infection you need to create a solution. In a one liter bottle fill one cup of water and fill up the rest using Pedialyte that contains zinc. Also add 1 activated charcoal tablet after you have crushed it well. Now using a syringe feed 10 ml doses of this solution to your dog. It is necessary to administer 10 ml doses every 15 minutes.
If your dog shows signs of improvement within 4 hours administer 10 ml doses every 30 minutes.
Recovery will become apparent within 8 hours after which you should feed boiled rice and broth to your dog. This diet should be continued for 3 days after which soft food should be fed.
After the infection is cured disinfect the floor and all other objects your dog came into contact with as parvo is extremely contagious and the infection may reoccur
Parvo can be deadly, I would suggest you find a low cost clinic in your area and get the dog in for evaluation, maybe it isn't Parvo at all. I lost a pup I adopted from the pound many years ago, was supposed to have had all of her vaccinations.
How old is your dog, did he receive his Parvo vaccine along with his Rabies?
Considering the extreme seriousness of a possible Parvo infection, the first thing you really need to do if at all possible is to at least obtain an official diagnosis from a Vet to determine if the condition is in fact Parvo or something else. The diagnosis will cost you far less than additional treatment; however the Vet may very well be willing to work out a time payment schedule for you which you might find affordable for treatment. The first thing to do is to make a telephone call and inquire after explaining the symptoms displayed by your beloved dog and your financial situation.
Something to consider as a home treatment, which would be my choice, is the use of colloidal silver which kills both bacteria and viruses. Prior to the development of the pharmaceutical industry and the development of commercial antibiotics, it was used extensively by physicians as a natural and effective antibiotic. An excellent article about its use to treat Parvo, and an accompanying video is at the following Link:
Note that the author recommends a colloidal silver of 10 ppm's (parts per million). However an excellent colloidal silver, which is the choice of many alternative physicians and which I use myself, is MesoSilver which is 20 ppm,s. To read some testimonials about its use go to the above Forum entitled Alternative Therapies and read my Post, "Colloidal Silver dosage". However, note that the information is for its use with people and not dogs or other animals. You can read more about it here: https://www.purestcolloids.com/mesosilver.php .
Also keep in mind that it will still cost you some money just to purchase it. Click this Link to get an idea how much: https://www.purestcolloids.com/mesosilver_price_list.php#ProductsMenu
Therefore I suggest making that phone call to the Vet as explained above before doing anything else. Remember, veterinarians love animals every bit as much as we love our pets, and their human side, as well as that of their influential office help, can sometimes be very accommodating. Good Luck.
Colloidal silver for parvo. Mix some 25 ppm in the dogs water bowl. Start with a tablespoon or two. It has no taste and the dog will like it. I would also suggest a good quality oil of oregano but it would be a chore getting the dog to take it, perhaps a few drops in a capsule might work..