Vet wants us to switch to prescription kidney diet - looking for advice

Just got some rough news at our last vet visit. Our 9 year old shepherd mix Charlie had his annual bloodwork and his kidney values came back elevated. Nothing severe but vet wants to start him on a prescription kidney support diet.

She recommended Hills k/d but wow the price. Ive been feeding him a pretty decent kibble his whole life so this is a big adjustment financially. We do have pet insurance but it only covers accidents and illness treatment, not prescription food apparently.

Has anyone navigated this? Is the prescription diet actually that important at early stage kidney issues or is there a more affordable approach? Not trying to cut corners with my dogs health i just want to understand our options.