I can sympathise Flakecake...Dental costs are huge!Fortunately now my cats both prefer dried food to wet.
I have 2 cats, both indoor, both rescue cats. They average out about £5 week cat litter. They are on dried food - for some reason don't like the wet - and this does tend to go far £8 per week sometimes less.
Vet Fees..this is where the cost lies!
I did have insurance but cancelled this after a couple of years. A word of warning for insurance..
Check the exclusions and small print before you buy. Everywhere offers insurance these days and I was wet round the ears when I got mine...
I paid out £600 on dental surgery for my cat - the small print in the insurance said dental surgery not covered. In fact anyone with insurance for their cats check it now if you haven't - I asked my brother to check his and, even though it was through a different company, the policy was practically word for word the same as mine.
Apparently one of the most common problems for cat's are teeth and it is linked to more serious ilnesses.
I took my poor girl to the vets when I noticed her coat was becoming more knotted and duller than usual and she wasn't grooming as much. Vet checked her mouth first and, at that point, she needed at least a couple of teeth out. Poor thing, when I collected her after surgery she had to have 10 extractions..
She must have had more teeth out before I got her from the Animal Shelter as she only has 5 now (but manages very well!). Anyway, after picking myself off from the floor and getting the credit card out, I checked my insurance...I was amazed at how much it DIDN'T cover...

so I would advise if you do take out insurance, check everything before you buy!
It was worth it though as she was like a new cat..well, a new cat would have been cheaper but not my Lucy!