I have several folders on my G: drive (G: being my 750GB USB backup drive) that hold MP3/Flac files. For this exercise it is the only drive I now have that had the space to store another 40GB folder. Searching for MP3 would have bought up every instance not just those in the one folder, G:\MP3\, that I wanted to delete. I would have to be very careful what I selected in the seach dialogue before pressing the delete buton.
I can see that the software you are recommending would have done the job. But it is unlikely that I will be doing very much of this kind of searching in future so the expense will not be worthwhile. I will use my work around if necessary.
Work around: move all the data on a drive that is bigger than the required space i.e 40GB+ my F: in this case, copy the MP3 folder over to F: do the searches, delete, move the now fileless folder back to G: and move back from G: the data for F: