I have no experience with dry shampoo, but I did a little research, and found this article pitting baby powder and cornstarch against Bumble and Bumble dry shampoo, which had a lot of good info: http://www.hairboutique.com/tips/tip543.htm
Most of the other brands I saw during my brief cruise around Google seemed awfully pricy, but maybe a little goes a long way? And, depending on your hair color, you’ll want to be careful—if you have dark hair, some brands (like Bumble and Bumble) come in different colors; others are really best for blond or gray hair.
Okay, would love to hear from someone with actual experience in this, but hope that helps.