I have a lot of pets. By a lot of pets, I mean I have 5 cats, 2 large dogs, and 4 chickens. While we're not exactly struggling financially, things are tight. Having pets doesn't need to be expensive and your pets don't have to suffer. We feed everyone the best food we can afford (cats get 4Health, dogs get Diamond Naturals, chickens get basic layer feed/scratch from the feed store), good quality litter, and good quality toys.
I very highly recommend learning some emergency care for your pets or learning how to administer medications. We keep stock of worming pills and worm about every 3 months. We use Advatange Xtra Large Dog for flea control on everyone (DO NOT USE K9 ADVANTAGE ON CATS, only REGULAR Advantage!!! There is a guide online for cat dosages.) If there are any injuries, I assess the damage myself. Most things I can treat at home with an Epsom salt rinse and iodine, followed by regular treatments of Vetericyn. It's not for the squeamish, but it's saved me tons in vet bills. If you have any questions, you can always call a vet for no charge. If you're uncomfortable with any of that, don't attempt to do anything yourself. As always, consult a vet first.
A great place to get pets fixed is at the local humane society. Cost us about $45 per cat vs the $95 at the cheapest vet. Dogs are generally more expensive the bigger they are, so keep that in mind.
All in all, I spend about $200 a month for everyone, but it doesn't have to be that expensive. The chickens honestly pay for themselves - they're $20 of the $200 and we sell the extra eggs to people at my husband's work for $3/doz and we get 2-3 eggs/day. I would not trade my critters for the $200 any day. I love all of them very deeply and their companionship has gotten me through the worst, including the time I was suicidal (after all, who could take care of my favorite cat as well as me? He wouldn't understand why I left him, either.) Pets don't have to be expensive unless you want them to be, barring emergencies. (In my state, CareCredit will cover pets!)