OP,
Look for reputable independent diesel repair shop. The price should be a lot less than a Ford dealer.
I am suspicious of the $6900 estimate. It seems low from a Ford dealer, based on what I have read others have paid a few years ago.
A few years ago I read about this repair on a Duramax (I know, different but similar) and injectors cost about 800 each (8x800=6400), plus the High Pressure Fuel Pump, fuel lines, etc. I think everything downstream of the fuel filter must be replaced.
I just did a quick search for parts prices from a Ford dealer and found injectors for 300. So it looks like those prices may have come down from a few years ago.
Check around, get more estimates. And good luck.