We have dog insurance on our two dogs. I think it's $80-100/month combined. They're still younger (5 years) and we didn't want to have a "Do we spend X amount on one or do we have to let him go?" situation. Food is probably another $500/year for the good stuff. This is for 2 terriers (20 lb and 30 lb). Add in the miscellaneous treats, toys, fun stuff and we're probably around $2,000/year. Give or take.
But they are so awesome that I don't even think twice about the cost.
I'd also like to add that if you can, 2 dogs are nice to have. They keep each other company, play together and I think it makes them happier. My wife got a dog when we first started dating and we eventually picked up the second one when a friend needed to relocate his. The first one definitely seems to be happier. Especially on days when we have to leave for the better part of the day.