The higher quality cases would be the zoloworld cases & i would say the better case.
The cheapest case around for MOTU would be the protech 55cents each but work well.
i just got 100 cases for my loose figures . i got them from theearthtoymall.com/sofcashotwhe.html. they are made for hotwheels but fit all vintage MOTU except Round back Two-bad. they cost $55.00USD for 100 cases + shipping
Note: i got the black permant marker off the bottom of king hsss & whiplash's feet(initials BB) if you can see it in the pic, using a sponge called 'White Magic', it works well to clean figures & you just need to use water.
I use zoloworld for MOC