Midway sells the Frankford Arsenal digital scale for about 30 dollars. Having used one for several years as a backup to my RCBS beam scale I am well acquainted with it's flaws and it's inherent accuracy.

While distinctly cheap it is actually an accurate scale. However it is only truly accurate for about a minute after you first turn in on. As the circuitry "warms up" the zero will start to drift in a sinusoidal pattern and that drift can be as much as +/- 0.3 grains. My normal procedure is to set my beam scale, tune in my charge weight on my powder measure and to insure I have set the beam scale properly I'll fire up the Frankfort scale and dump the pan from my beam scale to confirm the weight shown for both scales match.

Now, you are going to be measuring in Grams, which the Frankford scale can be set to. Keep in mind that there are 15 grains in 1 gram. So to get an idea of the level of accuracy in grams take that 0.3 grain deviation and divide that by 15 to get the deviation in grams. BTW, that work out to a deviation range of 0.02 grams, or 2/100 grams. Quite simply it is more than accurate enough for what you want to do.

Tip, the scale is set up to Auto On the display light at start up and I always turn that light off to conserve the batteries. I also have a gut feeling that turning the light off reduces current draw and may reduce the amount of that sinusoidal swing in the zero for the scale. Also, be careful to NEVER overload any digital scale. Because doing this can damage the transducers and totally grenade the accuracy of the scale.

I will also note the maximum capacity for this scale is 750 grains or 50 grams, so if you need to weigh out more than 50 grams of that protein powder you may have to do multiple measurements.

Following is a link to the Midway listing for this scale. Take note that it comes with a calibration weight.

Frankford Arsenal DS-750 Electronic Powder Scale 750 - MPN: 205205

PS; more than 40 years ago my brother and I had a friend who was born with broad spectrum food allergies, meaning he was "sensitive" to almost any food substance you can name. For the first 4 years of his life the only nutrient he could tolerate in volume was Human Milk. Over a period of many years he was gradually given different foods in tiny increasing increments until about 18 years where he could eat just about anything except shellfish. So what you are doing for your child really isn't as new as your doctor may have led you to believe. What is new is that this type of therapy has been expanded from something prescribed only for true desperation cases to those with more narrowly defined food sensitivities such as peanut allergies. Quite simply what you are doing WILL work.