I did a test on a normal default plywood Prim cube. I originally entertained the idea that by setting the sides to invisible, perhaps the display cost of the prim would shrink. Actually i found the opposite.
|Default Prim has a display cost of 389|
|Setting the faces transparency to 100 added 15 making display cost 404|
|making just one face 100 transparency ads the same amount of cost|
|removing the textures deducted 120 from the display cost showing how much a texture can change|
the cost your object has.
|Changing the size of a prim seems not to change the display cost unlike a mesh object.|