Dog with kidney problems

A custome of mine has a dog with Kidney problems and the vet has put the dog on "Hills prescription K/d food which she can't really afford, is there anyone out there who has a dog with this problem and is there a cheeper option of food,i have offered to let her have it at cost, but it is still to expensive for her, she doesn't want the dog to suffer but is out of work and the dog was a rescue one in the first place

Thank you