I would get the VOXL Multiplayer Voxel sandbox ($40),
and for programming I would get the Playmaker visual editing system ($32.50)
Playmaker is an entire topic in itself, and lets you make state diagrams to connect objects together. I figure it would help whip up some Minecraft-style behavior rapidly. (There’s a learning curve to every tool, even those that will end up saving you effort!)
I have $28 left over for later, when I have a better idea what is missing from the stuff I’m buying. 