The Amplifier: Pyle PLMPA35 2 Channel 300 Watt Mini Amplifier with 3.5mm Input was about $18
. The speakers: Pyle PHSP4 6-Inch Indoor / Outdoor 50 Watts PA Horn Speaker were $17.00
. The battery was $20
. 50ft 3.5mm Stereo Headphone Extension Cable - M/F $4.29
Everything was bought on Amazon.com.
I plan on painting the toolbox white. I used 3.5mm ext. cords to run speakers out, quick and easy.
The application I use on the I-phone is "Snow Goose E-caller" https://itunes.apple.com/us/app/snow-goose-e-caller/id498488885?mt=8 $1.99
To make my battery last, I use a Mophie Juice Pack to power the phone.