[regularfry]

The way I express it is that estimation is fundamentally a design process. You can't get an estimate without doing design work, to some appropriate level of detail. That design work is not going to spring forth from the void unbidden, so it needs to be paid for.

This does not mean that you need a big design up front, but it does mean that you need to be happy with a level of precision to the estimates commensurate with the funding that has been given to the design process.