Brag about what? Please take a moment to read my comment with understanding.
And the dollar sign goes on the side I put it: nine hundred thousand dollars. The fact that you want to write $900k is just an idea specific to the finance world (such as using parentheses for negative numbers).
Dollar sign goes before the number, cent sign goes after, other units go after: $7, 7¢, 7 lbs. You can’t pretend convention doesn’t exist just because it’s weird! That’s why it’s convention and not common sense.