We have 6 dogs so it's pretty eye watering. One is very old and one is epileptic so lots of medication required. Even though I'm a vet they are all insured. I treat most things myself and only pay cost price for drugs/materials at work which saves a fortune. We're absolutely on the high end of the dog expenditure scale but we can afford it and it works for us. As a rough idea:
Insurance: £210
Food: £300ish (mostly raw)
Medication for the oldie not covered by insurance: £60
Co-payments on the epileptic one's insurance as we have constant running claims for medication and blood tests: £20ish
Supplements (Riaflex, salmon oil, Yumega, CBD and MCT oil for the epileptic, Nutramind for the oldie): £80ish
Treats/chews (all natural stuff): £50ish
Worming/tick treatment: averages maybe £10/month across the year
Then there's toys, shampoos etc. that we buy as and when. They all have multiple collars, leads, harnesses, Equafleece jumpers, drying coats etc. I replace these when necessary or just buy more if I see something I like. Plus running a separate chest freezer just for the raw food. Plus the 2 big cars we run to transport them in, both with double Trans K-9 crates at £700 each.
I do gundog work and competitions with them, I'm not even going to begin to add up costs of fuel, entries, hiring facilities for training, gear etc.
'Unexpected' costs can be £0 or hundreds in any given month. I had to put two new insurance claims in last month in the space of a week, one for the cat and one for the elderly dog, so had to pay two excesses of £100 each, and there'll be a 20% co-payment for the dog as well.
Fortunately we never need dog walkers or daycare, I work part time and DP can WFH most of the days I'm at work. Any days we're both out at work or when we're on holiday, my DPs (retired, fit and active, also have dogs and live 2 minutes away) look after them.
We also have a cat but she's a lot cheaper than the dogs 😄