Caerus

So, I'm looking to power some speakers near a beach-volleyball outside my dorm. Unfortunately, I'm not exactly sure how to get speakers out there. I have a decent pair of speakers that I would love to use, but they need AC power to run. Does anyone have any suggestions? I know I can purchase a "Power Pack" for pretty expensive, but I am a poor college student after-all! Haha. Anyone have any suggestions short of running an extremely long extension cord?

Thanks!