You can buy Blue Gold cleaner from almost any scuba shop but they charge upwards of $100 a gallon for it. I've found it online at thecryoshop.com for about $44 gallon. It's very concentrated so a gallon goes a long way. There's places that sell it in 1 quart containers also, about $20. It's very hard to beat the price that I get it for.

Both Steve and I use it to make metals "Oxygen Clean", meaning no hydrocarbons. It's a very safe product compared to other degreasers. It has an indefinite shelf life as far as I know and you can re-use it if you're just cleaning parts, I put an oil soak pad on the top of the pan when I'm done to pick up what floats in solution.
Len