So, any recommendations ANYONE puts on here, especially with mine, I'd recommend you running by your vet first, just in case.
Let him/her know your budget may not be able to afford the current diet and see what he has for a recommendation as well!
Purina Pro Plan used to make an "on the shelf" - without script, urinary tract/ renal diet for cats and they may also have one for dogs- worth checking your local pet stores to see if it's still available. This same company (Purina Pro plan) also has a prescription diet called NF for kidneys, (I thought it was UR - but was quickly corrected), and WITH script can be ordered either by your vet if he's willing to order for you OR on sites like chewy. IF your vet thinks this is a good option the brand is cheaper than Royal Canin.
I will add that Purina is not as high if a quality grade of food than Royal Canin, which I think should be considered, BUT would be a better option than switching to a diet Not specified for Urinary Tract/Kidney functioning.
EDIT: HERE IS A LINK WITH A LIST OF FOODS FOR DOGS WITH KIDNEY DISEASE. THERE IS A VERY DETAILED ARTICLE ABOUT EACH FOOD, AND HAS AN EXPENSIVE RATING AS WELL AS QUALITY RATING. Pics attached FROM this sited website https://topdogtips.com/best-low-protein-dog-food/
Please give the site community time to give you other recommendations, run any ideas you consider by your vet, and make sure when you switch to do a gradual change (mix in new food with old food slowly over time, eliminating the old diet eventually). Stopping abruptly may make your dogs tummy upset, and you'll want to make sure your dog is eating it well, tolerating the change, and that his Urinary/Kidney health remains the same or gets better instead of getting worse- is his urine darkening, smelling pungent or have blood in it? Is his stool runny or bloody? Discontinue new diet change.
From 15 Best Low Protein Dog Food Brands for Kidney Health
You never want to switch your pet to one of the best low protein dog
food brands without consulting your veterinarian. All low protein
diets have a different amount of protein. Depending on your dog's
individual needs your vet will prescribe the right food. Many of the
best low protein dog food blends are only available by prescription.
Kidney disease in dogs is a very serious issue. However, it's not the
only reason to consider low protein dog food as other health problems
may also be a good cause for concern with changing your pet's diet. If
you were unable to pick a good low protein food for your dog in the
above list, here are ten more alternatives you should consider.