You'll find the original cost of change curve on page 40 of Barry Boehm's Software Engineering Economics (1981).
I scanned it this morning, and here it is:
I scanned it in sideways and I'm not very good with computers so I couldn't figure out how to straighten it.
That said, notice a few things:
1) There are 2 curves - one for big projects, one for smaller projects.
2) It's the cost-to-fix or change, not just the cost of change. It applies to bugs and changes.
3) It you look along the x-axis you'll see phases, not time. The projects used to gather the numbers were waterfall projects.
The book gets more interesting when you look at it's opposite page (41) and see this:
Incremental development is describe on page 42 as having been used as a successful refinement of waterfall on extremely large projects, such as a $100M project done in the 1970s, as well as smaller projects like Boehm's own project (I think) which was used to build a COCOMO calculator.
I've been meaning to share this for, oh, about a decade so sorry for the delay ...
Now, some help, please: how do I describe the scaling on the Y-axis (which takes the curve and makes it straight)? Is it logarithmic?