I can't find a way to display a number with a space between the currency and the number.
If I use the follow syntax:
select to_char(99.90,'FML90D99') from dual;
select to_char(99.90,'FML 90D99') from dual;
ORA-01481: invalid number format model
You can use this (by defining your currency):
SELECT to_char(800, 'FML999G990D00', 'NLS_CURRENCY=''$ ''') FROM dual;