If you just want to measure the current, get 1% .1, 1 and 10 ohm precision resistors, put them in the circuit one at a time, and measure the voltage drop.

If you want a permament meter, use the .1 ohm, and get one of the cheap volt meters which run on a 9v battery. Set it accross the resistor, and set it to one of the low ranges.

Resistors are available from Mouser 71-RS5-.1 etc. I think Circuit Specialists has the best deal on Meters.

Good luck