What makes an amp expensive?

Excuse me, could you elaborate on what factors contribute to the high price of an amplifier, or "amp" as you mentioned? Are there specific features or technologies that drive up the cost? Are there any notable brands or models that are particularly pricey due to their reputation or quality? Additionally, how does demand and supply play a role in determining the price of an amp? Understanding these nuances might help shed light on what makes an amp expensive.