That right there wouldn't get you very far. If I heard of any shop jacking prices just for Easter I'd go the other way. Can you say price gouging?
The specific sales concept in question here is time utility, but you could probably break it down to a simple economic concept called supply and demand as well. It's pretty much the most basic law of sales lol.
If Yukon parked their truck down the street and sold them at whatever price they wanted, that'd be one thing. But to have a shop sell a shaft at one price all year long just to jack them up for EJS?
Right. The shop doesn't stock the shafts all year long, they would have to make special arrangements. Businesses have a right to recoup additional costs for special circumstances, and you have a right not to buy from them. If you don't want to pay for the 10% upcharge for an onsite part during EJS, you're welcome to have one shipped from the supplier directly to your hotel room in 3-7 days.
Personally, If I knew of a shop that went out of their way to incur some additional costs and work to ensure that there was a supply of hard to find parts available just for Easter, I'd be very thankful for them. I've been stuck in Moab without parts before and had to drive to SLC and back to get them. I would GLADLY pay an additional 10% for a part to be available locally. Hell, I'd pay double in some situations.