As usual, I choose quantity over quality.
Assuming that we don't already have a shed full of bikes...
1. 84 KDX200. A really good one is $1500, making them probably the best bang:buck of any pre-85 bike. Good enough for VMX at my skill leveling.
2. YZ250A or Ossa Phantom. Haven't looked carefully at what they sell for in the post GFC world, but am assuming that $8000 will get a good one.
3. Side pipe CZ. $5000 gets a good one, right?
4. Some $500 crapper - gotta have a project, right? Probably a pre-78 125.
If its bikes in addition to what's already in the shed, then scratch the project and the KDX, and replace them with a decent 84 KX125 or something.