wiring a 5v digital voltage meter

I need help wiring a  voltage meter into my car for monitoring the voltage by my amps.  as always instead of paying $50 or whatever for stinger one or somthin, i try to it my way ( just as good but cheaper).  

Im not sure if some kind of resistor or relay would work but i figure if anyone knows its probly some one on here...  heres the ratings:

input ( to power the display) DC 5V, <80mA

input (it reads) 0-200V DC

 its supposed to be accurate to +/- %.02

by the way, by voltage meter i mean a digital voltage display.

ive been looking around my house for any kind of power supply, the closest i could find was a sony discman one thats 4.5v  500mA i dont want to fry my display though...  i'd have to use a inverter if i wanted to use it like that too.. 

either way id wire it to a acc/ ignition so its only on when i turn the key.  they guy i bought it from just told me to get a 5v battery for it but i'd rather do stufff the hard way so it comes on when i turn the key...

5V is no problem, if you are trying to use a cheap DMM type thing it probably wont work unless the voltage being measured is isolated from the power source of the meter, you could give it a try though nothing to lose

4.5V 500 mA should be fine if it is 4.5V many times they are rated at load.

its not a DMM, its a digital voltage display..

theres got to be a way to wire this