Lots of people have provided details on some setup costs (litter box, scoop, pet furniture, carriers (recommend one for each), bowls, spay/neuter, vaccinations, etc etc etc) so you don’t need to hear that from me. In the last few years (since I have been tracking) I’ve not done flea and tick meds because I lived in the dry west and fleas and ticks were relatively uncommon, but I might need to start this coming spring now that we are in a humid climate with lots of ticks. (Tick borne diseases are no joke, and fleas and ticks can absolutely get on them even as indoor only animals because they can catch a ride in on us, and it sucks.) I’ve used Feliway when I’ve had prior multipet households when introducing new animals, but my current two are littermates and don’t need it. It absolutely is worth it though (even if it is pricy).
This year my average monthly costs have been ~70/month. However, they have not had their wellness checks this year because of REASONS. Their vaccinations (rabies and FVRPC, both recommended despite being indoor only (and rabies is legally required)) are 3-year vaccinations now, which is nice. Last year I had an additional ~$1700 bill, which was their annual exams + vaccinations + bloodwork (which I typically have done every year to have a good baseline and to catch anything as early as possible), PLUS the Derp needed a dental PLUS multiple extractions, which was a lot. The previous year their annual exams + vaccinations + bloodwork was ~$340 for the two of them. So far, neither of them have needed emergency or off-schedule treatment at all.
The above includes food (high quality kibble + canned), treats, litter, + incidentals (a cat tree this year, might need another litter box (it’s recommended to have n+1, though I’ve generally gotten away with just n), I’d like a new pet fountain, etc.). I don’t buy many toys, they like playing with random shit generally, plus my parents sometimes send stuff. I highly recommend the Cat Dancer though. 1 million percent. Also highly recommend a pet fountain, especially if they are on dry food or partially on dry food. Cats are desert creatures (or evolved from them) and traditionally got nearly all of their water from their food, and some cats do not have a good instinct to drink, which can cause problems, and flowing water can entice them to drink more.
I am a BIG BIG BIG proponent of regular medical care, my pets are members of my family and I want them to have the happiest, healthiest lives they can. This includes dentals if they need it. Dental disease in pets can be extremely painful for them. It’s a crap shoot though how much they will need - some cats have a lot of trouble and some have nearly none. I’ve had 2 cats with essentially perfect teeth that only needed a dental a few times in their lifetimes, one cat that had terrible teeth when I adopted her at age 4, and one that we thought had stomatitis (which would have been bad news for his teeth) but which it looks like not to be the case - but he will likely need a dental every year (or nearly). Dentals are tough because they have to be anesthetized, and if they need extractions that’s extra.
Treatable conditions are also something you can’t really predict in cats (except maybe purebreds, IDK if it is as prevalent as in dogs). My first cat was very healthy until age 6. She got an infection in her mouth (unclear how, but she might have bit something sharp and it got infected). She was prescribed steroids to help with the inflammation and within a few days (maybe even 1 day?) went into severe distress. She had undiagnosed undifferentiated myelopathy (a heart condition not caused by a physical defect). Cats with myelopathy can’t be on steroids, it puts them into heart failure, and if I had waited even 24 more hours from when I got her emergency care she probably would have died. Her condition was treatable by putting her on low dose diuretic (to minimize any water retention, which can happen with myelopathy) and low dose blood pressure medication (to reduce stress on her heart). They were inexpensive (maybe $30/month? I can’t remember, it wasn’t a lot). The vet said she might live a normal lifespan and have a normal life, or could have a much shorter lifespan, but it couldn’t be predicted. She lived a normal happy life for 7 more years. Her last year of life was complicated by the fact that she could not be on traditional steroids, but until then her condition was 100% treatable and her quality of life was excellent.
My second cat, in addition to winning the genetic lottery for terrible dental luck, developed IBS, also around when she was 6 or 7. Her IBS was not treatable with diet changes (boy did we try) but was 100% treatable by low dose steroids, and she also lived symptom free until she was almost 14. Her medication (prednisolone) was around $21/month. Near the end of her life her symptoms became much worse and meds didn’t help, but for the entire rest of the time she was a happy cat who ate normally and played and was the best and her quality of life was excellent.
My current cats are around 3.5 and aside from the stomatitis scare (and the fact that the Derp probably needs annual dentals forever) they are healthy (touch wood). Since they are so young still, if they developed a condition that was possibly treatable and which their quality of life was still good, I would likely pursue. If they were older, or if their quality of life was not very good I would have to think seriously about what to do. Things like cancer or kidney failure can be really difficult to treat, impact QOL significantly, and be very expensive on top of it all. Things like thyroid issues, diabetes, IBS, heart conditions, can be managed very well and lead to normal QOL. (Well, until they can’t. But, it’s pretty obvious when that happens.)
I self insure because I can pay a $2000 vet bill and be ok. If I couldn’t, I would consider insurance.
(Oh, I also had a dog who was very expensive, but she was a super senior when I adopted her at age 14, and although I didn’t necessarily know all of her issues when she first came to me I did know she was “old” (and therefore would likely have increasing issues). I just wanted to give her a nice comfortable life in her golden years after having been neglected for a long time. She lived with me for 3 years and I don’t regret spending the money one bit. But she was very expensive.)