These are the fans I use.
http://www.alliedelec.com/search/productdetail.aspx?SKU=70225876
Should be perfect for what you need, fit it right in the master chief helmet, the spot in front of your mouth, no worries it won't be close to hurt, and cut vents outside on the front, they look fine, and you're good to go.
Have it pull air in. I run on 3 AA batteries, rechargeable, and it will run for about 25-30 hours a charge. Keeps me from sweating and visor fogging.
One fan to cool them all!