Can Lactated Ringers be purchase anywhere without prescription from a vet?

our dog has kidney disease and we administer twice daily doses of 100ml Lactated Ringers solution. A 1000ml bag lasts 5 days; our vet charges $28 a bag, but I have seen this product listed on various sites for about $3.99 a bag! Our vet is testy when we have asked for a referral to purchase from an online pet shopping site. I don't want to burn the bridges because this vet saved our dog. Can I find it someplace without a referral??