440 heads whats better??

So without knowing more about what you actually have now it's pretty hard to say where the first $3000 should go. Do you expect to be able to drive the car for $3000? You could build a basic 450 horsepower 440 for $3000 with the 906's. But the chassis and rest of the drive train will need close to that before it's safe. What about the transmission? Torque converter? Exhaust system? Rear axle?!?

The best advice here has already been given, start with a good bottom end and work your way out. The biggest way to waste your money is to try to stretch it too thin or build a mismatched setup around parts you can get cheap or have lying around.