^^^
Let's say it costs $2500 to manfacture an amp. The factory sells it to the dealer for $5000. The dealer then sells it at retail for $10,000.
If you were the manufacturer, you would have to double the price of the fuse to the dealer and, the dealer in turn, would have to double the price of the fuse when selling the piece of equipment to the end consumer.
Now then, in the case of the high end fuse: The factory buys the fuse for $50.00 ... 50% of retail. The factory increases the price to the dealer by $100. The dealer then turns around an sells the piece of equipment marked up by another $200 to cover the new fuse.
As an end consumer, I would rather pay retail of $100 for the after market fuse than pay $200 for it placed in my new piece of equipment for me at the factory.