I listed the ES40 Emulator on the Ohloh website; they keep track of CVS changes to Open Source code, and give an indication of what it would cost to develop software commercially.
According to their analysis, developing the ES40 Emulator would have cost $ 487,616. I think this is a bit too much, but it's an interesting figure. Taken together all the Open Source software I'm running on various computers adds up to over 800 million dollars.
Check it out for yourself, go to http://www.ohloh.net/projects/12354, sign up, and create a stack containing the Open Source software you use. Don't forget to include the ES40 Emulator ;-)