go to walmart. Get a battery charger and a small 12V battery.
On a larger scale, I have a 95 amp @ 15V forklift charger, standard car battery and ZX2500.1 for powering a mobile setup (standard 20A socket can't get me the instant amps I need, so the battery provides that).
How big of a charger you need depends on your music. A 25A charger plus battery let me run about 2500W if it wasn't heavy bass music.