Best way to render multiple 3D GUI Elements?

I'm currently trying to render a simple item selection screen/inventory similar to that in Minecraft creative mode. So far I have been successful in overlaying a single cube onto the screen by using a second camera and selective culling.

What I am interested to know is what would the best approach be to doing this on a larger scale? I don't know much about it but it feels like it would costly to use lots of cameras, one per item in the inventory...

Any advice or insight you can provide are much appreciated!