In reply to:
No, the price nor the instrument matters, does it?

The key is does it glorify God. Now how that is worked out will reveal whether one goes towards truth or error in his interpretation of what is right in God's eyes. I have no objection to any type of instrument as long as it is used correctly for God's glory. The Corinthian church was reprimanded for there improper use of certain gifts in the church and Paul's reply was to do all-things decently and in order. Paul did not desire confusion in the church. Does heavy metal cause confusion in-the church or in the soul of man, et. al. I would have to say YES!

1 Corinthians 13:1 Though I speak with the tongues of men and of angels, and have not charity, I am become as sounding brass, or a tinkling cymbal.
MacArthur comments on this verse saying, In NT times, rites honoring the pagan deities Cybele, Bacchus, and Dionysius included ecstatic noises accompanied by gongs, cymbals, and trumpets. I believe that could also be applied to heavy-metal.

MacArthur, John. The MacArthur Study Bible. Electronic ed., 1 Co 13:1. Nashville, TN: Word Pub., 1997, c1997.

Reformed and Always Reforming,