“A lost opportunity is better than lost money” has been cited in print since at least 1919. The saying means that the lost opportunity may (or may not) have gained money, but it’s still not money lost.
 
“Missed money is better than lost money” has been cited in print since at least 2000 and appears to be a modern version of the saying.
 
 
Google Books
Putnam’s Investment Handbook;
A stimulus and a guide to financial independence
By Albert W. Atwood
New York, NY: G.P. Putnam’s Sons
1919
Pg. 296:
Of course if one is slow in the stock market he may miss many opportunities, but a lost opportunity is often better than lost money.
 
Google Books
Barron’s guide to making investment decisions
By Douglas Sease and John A. Prestbo
Englewood Cliffs, NJ: Prentice Hall
1994
Pg. XIV:
No amount of advice can supplant paying attention to what you’re doing and knowing exactly why you’re doing it. If you don’t know, don’t do it. Remember, a lost opportunity is better than lost money.
       
Google Books
Tools and Tactics for the Master Day Trader:
Battle-tested techniques for day, swing, and position traders
By Oliver L. Velez and Greg Capra
New York, NY: McGraw-Hill
2000  
Pg. 129:
So stay on the sidelines when the odds are not in your favor, and rest in the fact that “missed money is better than lost money.”
   
Google Books
The Market Maker’s Edge:
Day trading tactics from a Wall Street insider
By Joshua Lukeman
New York, NY: McGraw-Hill
2000
Pg. 109:
Remember, missed money is better than lost money.
 
Google Books
Short-Term Trading in the New Stock Market
By Toni Turner
New York, NY: St. Martin’s Griffin
2006  
Pg. 92:
Here’s another truism: “Missed money is better than lost money.”
 
Trading to Fund Mission Trips
Wednesday, March 18, 2009
Missed Money Is…
I know 99% of my readers know the ending of this saying (“Better than lost money”), but given my trades on JAVA today- I’m still apt to kick myself over missed money.
 
HotStockMarket Message Boards
beehivesjoe
Jul 12th, 2010, 02:38 PM
Synikk, hang a big piece of paper on your wall above your computer that says
“A lost opportunity is better than lost money!”
 
Arbor Asset Allocation Model Portfolio Blog
Investment Proverbs – Smart Sayings
September 15, 2010
(...)
A lost opportunity is better than lost money.