Formatting Excel cells (currency)

I developed an Add-In for Excel so you can insert some numbers from a MySQL database into specific cells. Now I tried to format these cells to currency and I have two problems with that.
1. When using …

Currency to string

Normally I would use string.Format() to get a formatted string.

But I got the requirement that all amounts should be printed as text and not digits.

i.e. something like:

Format(3000, “us”); // =>…