Reading magnets is a tricky business, even if you have an expensive magnetometer. Magnets do not have a uniform field, so a tiny movement of the magnetometer's probe will give a large change in the reading. I agree that absolute gauss readings are not as important as having consistent relative readings, so an inexpensive home built meter will get you most of the way there. About the only time that you really need an actual magnetometer with a probe is when you do pancake magnets, those are often stronger at one end than the other and turning them around can shave a tenth of a second or so from your lap times.
I have a link saved to an article on making an inexpensive magnet matcher:
http://www.coolmagnetman.com/magmeter.htm