I'm on the eve of adopting an adult dog. Rescue. We have $800 (yes) set aside for initial costs: adoption fee (~$350 from a foster home), food and treats, leash/collar, crate, bed, baby gate to give the cat a safe place, initial vet visit, and toys.
Excited as I am to have a dog in my life again, I really am dreading the cost. Pets are a huge financial gamble. My parents cat got into a poisonous substance and cost them $1,500 in emergency vet bills last year.
My colleagues seem to all be having expensive troubles with their animals in the last few months: emergency surgery for a cat ($3,000), emergency surgery for a dog ($6,000), heart failure, car accident, stepped on glass, ATE glass.
Then again, I got my cat for 50% off (twenty-five whole dollars!) and she's been a treasure, no issues. In four years I've spent a total of $1,200 on her, or an average of $300/year.