Here's what I posted on the other forum:
Dog food (raw) for my own two 20-22 lb dogs: $40-$50 a month (can be done for cheaper during a "bad" month by using more poultry and less red meat/fish...the bulk of the cost is from sardines and goat meat)
Grooming supplies/chews/toys for both dogs: $5 a month (I don't have very playful dogs, haha)
Heartworm prevention and flea/tick prevention for both dogs: $8 a month (factoring in months that I don't give anything)
Vet care and grooming for both dogs: $40 a month (factoring in yearly check-up/heart worm test/Lyme test, Rabies vaccine, and professional grooming)
Total for Sophie and Gracie: $93-$103 a month
Sophie and Gracie are 20 lbs each so divide that in half for one dog. Sophie was MUCH more expensive the first year (spaying, vaccinations, check-ups, etc.) and she also got Lyme. Gracie has already needed medical care (I got her a few weeks ago). So the monthly cost is usually the least of a dog owner's worries. I think you could do it if you planned ahead and saved for a while but I'd focus on your kitty for now (since she's new and has been needing to go to the vet).
Also, if I remember correctly, you don't have a car yet. I don't either right now but I have friends who are able to give me rides and I can get veterinary care and dog food very close to my house (walking distance). Make sure you plan for that too.
Where do you live? Some areas need flea/tick prevention and heartworm prevention year-round but others don't. I don't give anything over winter so that saves me money

. I also don't get vaccinations for my dogs besides Rabies now (they've gotten the others before, I just consider them "done" with them).
Oh, and I'd get a crate if possible. Small dogs are difficult to house-train and a crate is a lifesaver! I'd get that instead of pee pads, honestly. You also forgot heartworm prevention in your calculations.