As the LEED Reference Guide states, the accuracy and cost of an M&V program is influenced by:

The level of detail and effort associated with verifying post-construction conditions
The number and type of metering points
The duration and accuracy of metering activities
The number and complexity of dependent and independent variables that must be measured or determined on an ongoing basis
The availability of existing data collection systems (e.g., energy management systems)
The confidence and precision levels for the analyses.