http://www.redlion.net/Products/DigitalandAnalog/ProductFamilies/CUB5.html    These things are cheap and should do what you want.   Most are either battery powered or will work with 12 volts DC.  I never bought a volt or ammeter, but the counter/speed sensor CUB 5 is about $100.   You will have to set it up, but that does not require a degree in electronics.