After the newness has worn off a little, you might try getting a lighter and burning the inside of the glass. The coating from manufacturing will turn black. Then scrub the black soot off with toothpaste (not gel) and it will significantly reduce the fogging.
You can also get a small bottle of baby shampoo for use as defog. It's 50 or 60 cents in the travel size section of the drug store. Just refill from a larger bottle as needed. You're probably looking at 5 bucks for a lifetime supply. That's significantly cheaper than 5 or 6 bucks for a tiny bottle of specialty dive soap. Spit also works and it's free.
What he said. I burn mine with a lighter, scrub with toothpaste. N