A cheap anti-fog concoction is a 50/50 mix of Johnson & Johnson Baby Shampoo and water.
Required items:
Fill the spray bottle half-full with Baby Shampoo. Top it off with water from the tap; however, leave a little room so the mixture will blend when the bottle is shaken vigorously.
Spray a liberal amount of the mixture onto the area in question. Rub the mixture with a micro-fiber cloth until it disappears.
This isn't a no-fail solution, but it'll do the job decently for awhile.