Re: Awesome
There's a big range, from the one on Cassini which is 3kg (plus a boom to get it far away from the rest of the spacecraft), to the sort that gets used on cubesats which is a single chip on a breakout board (~5g), which is stuck on the end of a solar panel.
I think if you could sacrifice 50 grams, then you could fit a reasonably useful magnetometer on your spacecraft.