Man, send me the $500 and I will get you one!! Might even send you a second one because I like you so much
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Now, seriously, go here:
http://www.parkerndt.com/mg25.htm and check out meters. Since you are only looking for partial/low level residual magnetism I would say either the 5 or 10 would be sufficient. It should be less than 3 to be of no effect if I remember correctly.
You should not need the calibration certification for your purposes but if you want it you can still get the gauge and certs with shipping for less than $300.
There are probably other outfits even cheaper. You might try NDTsupply as well.
He Is In Control, Have a Great Day, Brent