for the record, a call to dir would look something like this:

 
#!/usr/bin/perl
use strict;

my $dir = "//server/share"; #or whatever
my ($size)=(
       (qx{dir /s "$dir"})[-2]=~ 
       /([\d,]+) bytes/
       );
print $size;
[download]

Not pretty but probably faster than recursing
UPDATE: changed directory i'm calling from a local to a share