I uses the standard kodak grey card all the while and it has served me well. I shoot RAW mainly and am a Nikon user thus it's pretty straightforward for me.
Activate the calibration for pre-set white balance, and shoot a grey card, filling up the entire screen
OR
Just shoot a grey card and use the image as a grey reference. This might be handy because it allows you to use different images as the lighting conditions requires
OR
Shoot the grey card and click grey on Nikon Capture 4.
It's pretty straightforward and doesn't require expensive tools. Quantum physics precision is unnecessary, it's accurate enough. If you like it warmer, just push up the red WB point in NC4 respectively and up the blue if you prefer otherwise.
IIRC, Kodak grey cards are like $25 for a pack of 2x 8in by 10in size and 1x 4in by 6 in size at Cathay.