Edit: Just finished reading the topic that linked to this...

Plus, this way I can mix the colors at night and store them for later extrusion. I've already prepped 4kg this morning

So after some contemplating on how to make it faster and easier to mix, I considered a home made and mostly printed rock tumbler to accept a 1 gallon paint bucket and a drill, but the hardware would have been close to $40....certainly more costly than a jar.
Then I realized that Home Depot sells a bit for mixing paint which uses a hex rod. While that would work, $5.97 was too rich for my blood since the head is just a plastic part I could easily print. Metaldrgn shared a paint mixer bit he designed here. I scaled it up approximately 30% and drilled the hole with a 3/8" bit and threaded a 3/8" rod into said hole. Mixing now takes 3 minutes.

In the process of mixing Indigo which is new to OS3DP

A custom bold orange for a friend, and an accidental "Autumn blend"

Indigo and burgundy. Both are new colors at OS3DP and I think I may be the first to play with these in the wild. Both were based off of private conversations with Jonathan after my mixtures with masterbatch ratios, so I will be posting reviews shortly.

Cost of printed material- $0.00 (sample roll from Coex)
Cost of paint can- $4.93
Cost of rod- $1.37
Since mixing with an old sauce jar is free, this was the best option. All colors shown were mixed for 3 minues with a drill. And while I don't have any pics of filament or prints, I can stand by this method as I am currently extruding the bold orange shown above and it is coming out wonderfully.

While I drilled a hole in the lid for the paint can, I would really recommend keeping it open for three reasons.
1) It's really cool to see how fast the color takes to the pellets
2) The lip on the can is about 8mm on either side from the internal wall and this creates a problem when dropping the mixing bit in. So while the force of moving pellets should eventually rub off onto virgins, it would be best to keep the lid off so you can angle the drill to maximize mixture. If you are smooth and steady, you will not have pellets flying out even when you have the drill power maxed out.
3) If you use the lid, the spinning rod may agitate the edges of the hole in the lid and drop some tin into the mixture. This is exceptionally bad news if you use a melt filter.

Happy extruding!