ok - so what you want is for {BALANCE} to not include the currency code in its output? OR better still something like {RAWBALANCE} which doesn't include it.
add this at line c. 697 of administrator/components/com_rsvppro/libraries/attendeehelper.php
$message = str_ireplace("{RAWBALANCE}", $attendee->outstandingBalances['feebalance'], $message);
and
$ticketintro = str_ireplace("{RAWBALANCE}", $attendee->outstandingBalances['feebalance'], $ticketintro);
at line c. 1371 of administrator/components/com_rsvppro/libraries/jevrsvpparameter.php and similar changes for $tickettemplate and $ticketfooter in the same file.
then use {RAWBALANCE} where you don't need the currency symbol