Clearly a case for sexeger. 
sub commify {
    local $_ = reverse shift;
    /\./g;
    s/\G(\d{3})(\d)/$1,$2/g;
    scalar reverse $_
}

[download]

Makeshifts last the longest.

In reply to Re: "Commifying" a number by Aristotle
in thread "Commifying" a number by Tanalis

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