I got one of these recently from banggood.com for $2.70.
http://www.banggood.com/Wholesale-Red-LED-Panel-Meter-Mini-Digital-Voltmeter-DC-0V-To-99_9V-p-49602.html
I'll use it with a solar project I've been tinkering with but it
certainly could be used in the vanagon.  It seems quite nice quality
to me and pretty accurate.  It reads about .1V low compared to my
DVM, which is not particularly high quality.  It holds that "error"
from 7-8V up to 28V which was the range of  DC sources I had
handy.  Current draw is 10mA or less.  I uploaded a photo to banggood
of the meter turned on and in my hand to give an idea of it's size
and brightness.  Enjoy!

Edward