Format Textbox as foreign currency

I've done some research, and I am stumped!
I am trying to format a form textbox as currency in £ (GBP) but can't seem to get it to work because my settings currency is USD.
The following converts the number to $ format:

Formula:

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I also tried this:

Formula:

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which formats the number to £ format correctly but enters the value as text into the spreadsheet, which won't work for what I need it to do. Help!

Bump- still can't figure this one out! Thanks for the assistance!!