I don’t have the answer Tim, but I 
to ask yourself the question.
(up his hat (like the smiley) is a French expression to say congratulation).
Just my $200, I will send you my bank account reference 
I believe this is irrelevant, for your client not make any difference if it was a Copy / Paste, or something very fast like this, for them is that the Software will function in your workflow and how long it will gain in productivity, in my opinion the rest is the rest !
Not to mention the time it took and still take researching and keeping my base constantly updated data, and that the customer will NEVER want to know.
I had the same problem as Tim…where each project that re-used code was getting done in less and less hours…so we implemented a value-based pricing on our projects and so far it’s been pretty good…We still do hourly on some things when it’s just a few hours. Most of my projects are anywhere from 40 to 120 hrs long…
As an accounting professional and having worked in public accounting for a number of years, we used something called “value” billing. This was employed whenever we did work that required a very special qualification (tax, audit, consulting, etc.) and allowed us to bill a client based on that special qualification. It was an objective amount, but there was no guilt involved in charging a client 5 or 10 times what our normal billing rate would be because of the special abilities that we brought to the task.
I don’t do a lot of client work when it comes to programming, but I do use a value billing concept when I do development work for a client because I know that they are getting the benefit of our endless hours spent developing commercial software. Our “value” comes from the special tools in our development process that allows us to get things done so quickly and we feel that billing for those over and over again is what allows us to continue to evolve these tools to be even more efficient.