The Brightroom Storage Container from Target is a nice alternative to custom acrylic cases for storing Pokemon ETB's, with dimensions of 8 inches in height and 8 inches in length, and 4 inches in width.
Note: These housed my sealed collection of ETBs for the last few years, so some may have slight scuffs or scratches, but overall are in close to or like-new condition.
This listing is for (4)containers, but there will be several available