I think this works if the $1 represents an extra bill that you didn't know was in there, but not if you looked more closely at a specific bill and were happy to realize that it was a $1.
How about this, then: if I don't have any ones in my purse, this is because I have spent them on things already (since in the past, my purse has contained singles, and that is the typical method by which they depart). Assuming I really want the M&Ms, I might resent the fact that I made other spending choices in the past that caused the lack of ones. Finding the one is news that I did not make (all of) those resented choices.
The other day I went to get some productivity-enhancement M&Ms from the candy machine at work. When I opened my wallet, I didn't immediately see a $1 bill. Then I looked some more and I found one, and I was happy! But of course that doesn't make any sense. If that bill hadn't been a $1, then it would have had to be a $5 or more, with an expected value of $5+, which is an amount that I certainly would not have paid for a bag of M&Ms, most excellent though they may be. This means that I preferred a bag of M&Ms to $1 (that's why I went to the candy machine in the first place), $1 to $5+ (I was happy when the bill turned out to be a $1), and $5+ to a bag of M&Ms (I wouldn't have bought them at that price). Not too surprising I guess, but still kind of weird.