The problem, IMHO, is not to find a unique standard measure for the software but some means tha permit us to know better what we are doing.
The Software metric world is not an easy word, and it could not be easy for a simple reason: the ICT Word is not an easy world.
The metrics help us to work better, but they will never be the solution of our problems.
I'm using COSMIC and IFPUG in the counting of the same product (for example using COSMIC FP to measure the batch stream and IFPUG to measure the Front Office functionality), of course you can not to sum them (it would be as summing apples to oranges).
Each measure can permit you to know the functional dimension of that piece of software. How to transform it in effort and cost this is another story.
To know the relation betweenthe functional size and effort and cost the best thing is to do a dirty job: to collect your historical data and to obatin your proper factors.