Lego sorting trays: conveniently stacks to a fraction of the size. By default it's 120mm across.

Print in vase mode 0.8mm, bottom no more than 0.8mm thick - tested with PLA, prints in about 1 hour per tray.

I've included the Fusion 360 file for people to play with, it's parameterised so you can change the overall width / depth / height and hole sizes. It will automatically recalculate the hole spacing (minimum of 5mm between holes), but it will need fixing if you change the overall size: just open each of the hole extrusion steps (warnings) and close it again and it should fix itself and the linked pattern will be fixed too (they'll be errors in red). The hole sizes increase by 50% by default, you can just just the smallest hole size and/or the size increase factor or just manually edit each hole size. I don't recommend going too big as the wall thickness stays at 0.8mm and it'll get a bit wobbly.