Code:
alias mp3stats {
  set %wild.card $+(*,$replace($$1-,$chr(32),*,.mp3,),*.mp3)
  set %all.mp3s $findfile(%mp3.dir,*.mp3,0)
  set %wild.total $findfile(%mp3.dir,%wild.card,0)
  set %wild.percent1 $calc(%wild.total / %all.mp3s)
  set %wild.percent.complete $calc(%wild.percent1 * 100)
  msg $active Total of %wild.total mp3s containing the string " $+ %wild.card $+ " which makes it $round(%wild.percent.complete,2) $+ $chr(37) of my %all.mp3s mp3s
  unset %wild.*
  unset %all.mp3s
}


*DURING TEST*

[1:20:43] [@Axl] Total of 103 mp3s containing the string "*Pantera*.mp3" which makes it 2.81% of my 3663 mp3s
[1:21:21] [@Axl] Total of 9 mp3s containing the string "*Korn*Away*.mp3" which makes it 0.25% of my 3663 mp3s
[1:21:52] [@Axl] Total of 0 mp3s containing the string "*Zorbas*Dance*.mp3" which makes it 0% of my 3663 mp3s
[1:22:00] [@Axl] Total of 1 mp3s containing the string "*Zorba's*Dance*.mp3" which makes it 0.03% of my 3663 mp3s


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as far as i can tell this script also works in subdirectories inside your "%mp3.dir" but im not 100% sure