I confess, I made a bad mistake some time ago. I started to work on a project that had no proper source control system in place. Instead, zip files with source code were copied back and forth and merging was done manually using WinMerge. And I did not take a stand and say: "I want a source control system or I'm outta here!". Not that it would have helped, but it is the principle that counts.
As a result I spent at least two hours every week merging code. And then the risk that something would go wrong and I would need to spend at least another hour to find out what was going on and correct the problem! As I have the memory of a gold fish (*) those were the two hours I picked up the phone saying "I call you back!" only to put it down without taking the effort to notice who was calling. People could have said my boss was standing outside giving free money to whoever asked for it without me hearing them, let alone being interested. By Turing, what a stress!
Now I'm in a similar project situation where we do use a proper source control system, in this case Subversion. If they are using a source control system in Heaven, I'm sure it is Subversion. Although not flawless, but what a blessing it is! But if you are using CVS, that's OK too. And there are probably more cool source control systems that I don't know of, but since I don't know them, who cares.
By the way, did I already tell you I wrote a white paper about how to use CVS in combination with JDeveloper? No? OK, I wrote a white paper about how to use CVS in combination with JDeveloper. You can download it from OTN. It is based on JDeveloper 9.x and perhaps a little bit outdated, but it still explains the principles of source control and what it can do for you. JDeveloper 10.1.3 already offers much better integration, also with Subversion. I hope to be able to write a white paper about that too. Maybe it helps when you call my manager and tell him you want me to write it. Just say the word and I'll give you his phone number!
Anyway, the point I try to make here is this. The effort of installing a source control system like Subversion and maintain it, is only a fraction of the time people spend on things like manual merging. And then the risk of things going wrong. Come on project managers, you can do without that! It is hard to give you exact metrics, but based on experience I dare to say you already crossed the break-even point when two people worked together for a month. After that, you definitely keep money in your pocket. And the developers are happier too!
And once you have it, you suddenly realize it offers opportunities you were not aware of they existed before. Like going back to a previous version (for example the one that is in acceptance test) on instant, fix an issue there and almost with one click of the mouse go back to the current version and move on. Or find out who implemented that one great feature so you can give him or her the medal of honor of the programmer of the week!
(*) Actually, the saying 'having the memory of a gold fish' appears to do great injustice to this fellow creature. If it's true what they say at Goldfish pass memory test I would praise myself fortunate when I would have the memory of a gold fish.