you will need:
a container (I got this tin from a pound shop, but you can use an old coffee tin or something and make this even cheaper)
a bit of wooden dowel, just slightly longer than the diameter of your tin.
Step 1: Shape the Dowel to Fit
Step 2: That's It.
I plan to add some tape to the dowel to soften the blows from the portafilter , and also I'll be adding a hinge to the lid, but it's not necessary.