On a V8 the heads do not need to come off. What needs to come off is the intake manifold. I just went through the same thing with my 2001 4.4 X5. Using all BMW parts, including the following it cost me $2200 = $1000 labor and $1200 parts.

1. Waterpump (and gaskets)
2. Thermostat
3. New valley pan (updated style)
4. Intake gaskets
5. Injector gaskets
6. Upper, lower and middle radiator hoses
7. Oil change
8. 2 new O2 sensors (went OEM Bosch verses BMW - just couldn't justify the extra $125 a sensor for the BMW logo)