It is "really" unusual to be told Your pup probably has canine parvo virus but for him not to be kept for observation in a veterinary clinic.
Canine parvo virus is serious and can be fatal, he needs medical attention as soon as possibe, a vet may be expensive but this is unfortunately a part of being a dog owner. If he is not seen to he could die.
I am not sure where You from but I know in the veterinary clinic I work in and many other in Australia you are able to pay it off if You're a regular customer or have been there before veterinarians are usually pretty good with that.
If he is throwing up it is not advisable for him to be eating while he is still throwing up if it is continued however or prolonged the best food would be boiled chicken. You should definately be keeping his fluids up, but I would seriously consider ringing around Veterinary clinics and checking if any have a payment system where you can pay it off near You. It is dangerous
If your puppy has Parvo they vomit and have diarrhea somtimes with blood and mucus.They can also run a fever.You need to keep as much fluids in him as possible .You need to make sure that he stays hydrated.How long has he been sick and what symptoms has he. Has he had his vaccinations?You need to call your vet and tell them what is going on they might let you make payments or they might be able to tell you how to treat him at home.Your vet would give him iv fluids and meds to help with vomiting and diarhhea and antibioics to help with any bacterial infection.Parvo attacks the stomach lining and is very painful.Usually with treatment they start feeling better within 3-5 days.Please keep us posted.You will be in my prayers.God Bless and Take care.