my $diff = $saldi{C} - $saldi{D};

##</code><code>##

my %saldi;
foreach $file ( glob "*.txt" ) {
    open FILE, '<', $file;

    my $data = {};
    while (<FILE>) {
        chomp;
        next unless /\S/;
        my ($name, $price) = ( split /,/, )[ 3, 4 ];
        next unless $name && $price;
        $data->{$name} += $price;
    }
    my ($datasetname) = $file =~ m/^(\S+)\.txt/;
    print "$datasetname\n";

    foreach my $name ( keys %$data ) {
        printf "\t$name\t" . "%16s\n", big_money( $data->{$name} );
    }

    # store it...
    $saldi{$datasetname} = $data;
    
    close FILE;
}

# now, you can access all data by specifying the appropriate
# pairs of keys, e.g.

printf "diff C-D: %.2f\n", $saldi{testdata}{C} - $saldi{testdata}{D};
# ...