Estimates

In general, when you want some work done - maybe car repair, you are advised to "get an estimate". As a home-owner, the general wisdom (albeit impractical to impossible in some cases) is to get "at least three estimates" to compare. In the software world, getting an estimate for creating software is far more difficult and elusive than estimates for tangible products.

See Software_development_effort_estimation, especially the 'humor' section.

The SCC tool (like sloccount before it) is great for at least quantifying the Source Lines of Code in an existing product.