I think I just found the solution:
IF(STAGE="Executed", {EST. VAL.},"")+0
That allows me to format the formula field as a currency.
And all empty fields show up as $0, which is perfect.

I think I just found the solution:
IF(STAGE="Executed", {EST. VAL.},"")+0
That allows me to format the formula field as a currency.
And all empty fields show up as $0, which is perfect.

The problem is the final empty string in your formula. That’s forcing the output to be a string, not a number. Long story short, the IF()
function only outputs a single type of data. If one part outputs a number and another outputs a string, Airtable will force-convert the first part to be a string for consistency.
The solution is easy: leave out that ending empty string. If that third argument is omitted, Airtable will leave the field empty.
IF(STAGE="Executed", {EST. VAL.})
The problem is the final empty string in your formula. That’s forcing the output to be a string, not a number. Long story short, the IF()
function only outputs a single type of data. If one part outputs a number and another outputs a string, Airtable will force-convert the first part to be a string for consistency.
The solution is easy: leave out that ending empty string. If that third argument is omitted, Airtable will leave the field empty.
IF(STAGE="Executed", {EST. VAL.})
That’s even better and so much simpler. Thank you, @Justin_Barrett