HA! You would think so, but it's actually been asked quite a lot of times around here.
1st, set the function.
'Function' > On (name your function) - 'Function' > Set return value to RegexReplace(Function.Param(0) & "", "(\d)(?=(\d{3})+$)", "g", "$&,")
Then -
YourTextBox > Set text to Function.Call("name your function", GlobalVariable)
From the 1st part (name your function) will be the same as the 2nd part ("name your function"
This will only give you the commas: i.e $1,000,000