As an FLL mentor this year, and several previous years, this is what I think i a minimum.
2 NXT kits. A third of fourth is great, but not nessisary.
Access to 3 computers, preferably laptops. 2 for programmers, one, or more, for research.
Field parts and
proper competition table with overhead light.
That is what I've seen as the minimum to be able to keep everybody productive. With less than this, the team members don't have the supplies to keep occupied.(with something productive)
Most of these thing are reusable each year, so once you have a good setup the yearly cost is minimal.