A compression and leakdown test will let you know how bad the problem is. Do you notice smoke behind you when you get on it? If so, your rings are shot.

If you don't replace them yourself, it will be close to $800-900 to fix it at a mechanic. I would get it fixed as soon as possible since it is roasting your cat, creating harmful sludge inside the engine, killing your 02 sensor, and putting your engine at risk for oil starvation.

Check out my thread that I created a while back when I had this problem and replaced the rings myself. It will give you some good info.