Ron:
1st line of the specs of the ebay item:
DC 50A Mini Blue LED Digital Amp Current Panel Meter
& Shunt
Unforunately 36 V is non-standard and they say < 50 mA but don't tell you at what voltage which is probably 5 ish. That's 0.25 Watts.
Again, just looking at two suppliers, I found a 12 V 25 W (10 x more power than needed) power supply that's EXPENSIVE and overrated for the application:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=RP30-2412SEW/N-ND, but it has the right input voltage range.
This
http://www.newark.com/tracopower/thp-3-2412/dc-dc-converter-3w-12v-0-3a/dp/51R5278 is a bit cheaper.
The 36 VDC and low cost digital are competing with each other.
The LM317THVT is a linear regulator that works to 57 V input:
http://www.futurlec.com/Linear/LM317HVTpr.shtml it's also available from other suppliers. This:
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_117621_-1 could become a basis (PC board) for the regulator. The voltage ratings of the caps need to be changed and the variable resistor changed to a fixed one and the LM317 changed to an LM317HVT. Still inexpensive. Probably won't work, because the ebay item say an "independent supply" is required. This means isolated.
If 120 V is available, then the power options get better and could be an inexpensive "wall wart".
The ebay item says a 75 mV shunt and 0.1 V resolution. If this were the case , the meter would always read zero. They may mean 0.1 A resolution. Asked seller question.