It seems kind of odd to come onto an enthusiast site asking that kind of question.
Expenses are going to depend on you. Your insurance will be different from mine or anyone elses for that matter, so no real help there. Gas usage depends on your ability (or lack thereof) to keep your foot in check. Maintenance is no different from any other car, really. Though I'm more inclined to use higher quality parts and fluids than most car owners, and I like to think it pays off for me. I spend ~$35 for an oil change every 3-4 months, and ~$80 for gas every month. I've had my current WRX for going on 7 years now and don't regret purchasing it, though I do wish I had gone for an STi at times. This is my second WRX.
You'll find that most of the opinions are going to be biased or skewed here, something you have to understand when asking these questions on an enthusiast forum, as I mentioned.