I don't need to do it on such a large scale for indoor plants, so I've been using the largest plastic salad bowl for mixing my soils
... and then storing them in plastic coffee containers once emptied.
One thing I found very useful though for the garden side of things was a 17 gallon tub with rope handles. You can find them at feed stores and online for outrageous prices for just a plastic or rubber tub. And then I found one listed for toys at Target that was only $7.88. I wish I bought more than one. But I found
Walmart still carries a version of it, it's one of my favorite yard things that I use. Easy to tote around when weeding or cleaning up without the larger bins that tip over, mixing dirt, wetting soil mixes, and it's sturdy enough to hold up outdoors. I'm definitely getting a 2nd one now that I found it again. So look around for something similar, don't stick to just gardening uses and hopefully you can find a cheap one.
