Pepboys, AutoZone, Kragen, WalMart, and other places. Roughly $8.99 for a bottle.

 

Alcohol actually does a good job at pulling water/moisture out of gas tanks as well. In fact good Dry Gas is mainly Isopropyl alcohol. The crappier stuff is made of Methanol and should be avoided.

Even then though, I'd stick with the cleaners specifially meant for car engines. They contain other cleaning agents as well, and will probably do a much better job.