We have a cat. Start up costs 2.5 years ago were around $1k. $500 non-refundable pet deposit, $120 shelter adoption fees, $200 vet visits (had to take him to the kitty ER a week after we got him), $150 in cat care items/toys/food/carrier/etc.
Ongoing maintenance costs are about $15 a month in canned food, $10 a month in cat litter, $6 a month in dry food (sort of a splurge item - $35 a 15lb bag, but lasts about 6 months), $7-8 a month in Advantage flea control. Cat is strictly indoor only, but fleas figure out how to get in anyway. I budget about $25 a month in health care costs in a 'cat hsa'. He is a young, healthy cat and needs nothing now, but the fact that he will need increasingly more health care as he ages as inevitable for him as it is for any human, so no time like the present to start planning for the future.
Irregular costs are mainly boarding. I think we pay something like $17 bucks a day for the place we take him. Other random costs are the occasional new toy or catnip.
He is a member of the family. We look forward to seeing him when we get home. On my phone, the background pic is of my daughter and my cat chilling together on the couch. He occasionally does things to annoy us like scratch the speaker covers, likes to piss on clean, unfolded laundry, and of course the time we found out indoor cats can have fleas too. But my daughter also has destroyed things, gets on my nerves occasionally, and costs money, but I'm not getting rid of her either. :p They both add value to my husband and I's lives.
Overall, I can think of bigger things in the way of FIRE than my cat.