Thinking about just getting this one. It's $8 and the AD584L. They also measure with a 6 digit calibrated multimeter, at all four voltages: 2.5, 5, 7.5 & 10V. And they share their results on the bottom on a label. All you have to do is dial in your meter to match their numbers.
Beware, not all meters can be calibration adjusted that easily. They might need specific voltages and all ranges done, not just individual.