49 Characters: 
sub a{$_=sprintf"%.2f",pop;while(s/\B\d{3}\b/,$&/){}$_}

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Update: 48 characters: 
sub a{$_=sprintf"%.2f",pop;{s/\B\d{3}\b/,$&/&&redo}$_}

[download]
--Dave

In reply to Re: Re: (Golf) Formatting Integer To Money by dpuu
in thread (Golf) Formatting NumberTo Money by enoch

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