I think Expodisc is very expensive for what it is. If you want to try something like that they I'd opt for the lid off a Starbucks coffee, works fine.
As Wayne said, there are various options, including using a neutral grey card as a target. Whatever method you use, you will still need to do a little tweaking afterwards.
In any challenging situations I shoot RAW with a fixed Kelvin setting (any setting will do, but I choose the one nearest the conditions I'm in) and I leave it like that for the whole shoot. It's then very easy to batch correct later in something like Lightroom.