I couldn't resist posting a solution that doesn't use split, even if it uses string eval instead:

use strict;
use warnings;

my $str = "aabceezazerrfde";
my %vals = ( a => 7, e => 2, z => 26 );

my $total = 0;

while( my ( $char, $val ) = each %vals )
{
    my $count = eval "qw($str) =~ tr/$char//" or die $@;
    my $charval = $count * $val;
    $total += $charval;
    print "Found [$char] $count times ($count * $val = $charval)\n";
}

print "Total = $total\n";
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Found [e] 4 times (4 * 2 = 8)
Found [a] 3 times (3 * 7 = 21)
Found [z] 2 times (2 * 26 = 52)
Total = 81
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