I find it peculiar that the file system is scanned twice. The following avoids that:

#!/usr/bin/perl

use strict;
use warnings;

use File::Find::Rule qw( );
use Path::Class      qw( file );

die "Usage: $0 path/to/search\n"
   if @ARGV != 1 || !-d $ARGV[0];

my @scan = File::Find::Rule
   ->name(qr/\.mp3\z/i)
   #->file
   ->in( $ARGV[0] );

my $last_dir = '';
my $fh;

for (@scan) {
   my $file = file($_);
   my $dir = $file->dir;

   if ($dir ne $last_dir) {
      $dir = $last_dir;

      my $m3u = $dir->dir_list(-1);
      $m3u =~ s/[\s.']+//g;
      $m3u = $dir->file("$m3u.m3u");

      open($fh, '>', $m3u)
         or warn("Unable to create \"$m3u\": $!\n");
   }

   print($fh "$_\n");
}
[download]

Untested.

Note that this (and previous solutions) will probably create an m3u named "..m3u" if you pass "." for argument and that directory contains mp3s. This can be solved by changing
->in( $ARGV[0] )
to
->in( dir($ARGV[0])->absolute )
(Don't forget to import dir.)

(Should have been a reply to the OP. The OP was notified.)