you have no idea what you are talking about Gill.
The price is all about volumes , warehousing & logistics
firstly JD get the mufflers made for them which are designed to work properly so they do not burn the grass, set fire to your mower or wake the dead when you mow.
because the numbers are lowish, the unit cost is high & usually they are paid for at end of the month after delivery
so the excess made for supplying replacements are paid for perhaps 10 years before they will be sold
then they sit in a warehouse costing a lot more to run than most people would believe , which is why a lot of on line retail drop ship because this can knock up to half of the delivered cost off the item
then finally your muffler needs to be picked, packed , invoiced & delivered to the dealer who also needs to make a profit on the sale