Average monthly cost?

I work at a shelter and have really fallen in love with a cat there with CKD. I’ve been thinking about taking her, but am worried about vet care getting expensive as she is declawed and prone to arthritis and also has stage 2 CKD. I do get discounted vet care through my job, but I’m wondering if anyone could give me a ballpark of what they spend monthly on their CKD cat? TIA!!