You sound quite naïve/inexperienced in keeping pets if you think that is all people pay for.
Yes, in theory all your cat should cost you is food, insurance, and monthly sundries, and most probably do while they are young, in reality cats and dogs can cost thousands, especially as they get older. Insurance goes up every year, and if you want to change insurer, then you are not covered for any conditions that the may have, some things like dental treatment are not covered. Special diets etc, flea worming and vaccinations, neutering. Not to mention the cost/faff of boarding if required.
Excesses also increase as the pet ages, to the point where the monthly premiums and percentage of excess exceed any amount you will ever end up paying out yourself if you didn't have the insurance.
We have a dog in our family that has a myriad of health problems, they don't affect his longevity but he needs medication to control his conditions. His monthly insurance payment is £250 a month, plus they pay 20% of any treatment he needs, as well as a special diet to not exacerbate his condition. if they didn't have the insurance they would be paying £450 in medication alone every month.
I've had dogs all my life, as well as other pets, it is a massive financial and emotional commitment.. OP should be getting one because she can offer it a good life, not so it can be used as a crutch to cheer her up on command.