Merchandise at a concert is priced far above what the same shirt costs anywhere else, and the reason is not simply that the buyers are captive. Several parties are paid out of that one sale before anyone counts a profit.
The venue takes a share of every sale
Most large buildings charge the touring party a percentage of merchandise revenue in exchange for the counter space, the staff standing behind it, the card terminals and the security around the cash.
That share is negotiated before the tour arrives and varies enormously by building. An arena with a strong bargaining position takes considerably more than a small club with an empty diary.
The cut comes off the top, before the artist or the merchandise company sees anything at all, so the sticker price has to absorb it in advance rather than afterwards.
Printing is a small part of the number
The blank garment and the printing together account for a modest fraction of what the customer pays. Design work, licensing approvals and sampling all sit on top of that base cost.
A tour commits to a print run months ahead of the first date, which means paying for stock in a size curve that is guessed rather than known.
Whatever fails to sell travels onward with the tour or is written off at the end, and that expected waste is quietly priced into every unit that does sell.
The stock travels with the production
Merchandise moves in the same trucks as the staging and lighting, taking space that has an alternative use, and it must be counted in and out again at every single stop.
Sellers are frequently hired locally, and the building's own staffing rules often decide how many people can work the counter and for how long either side of the show.
Those costs are fixed per city rather than per shirt, so a quiet night in a half-full room makes each individual sale carry a much larger share of the overhead.
Scarcity at the venue is partly deliberate
Tour-exclusive designs, and prints carrying the city or the date, exist because an item that cannot be bought again later sells at a rate a generic shirt never reaches.
Short runs also reduce the volume that has to be hauled onward, stored between legs, or disposed of once the final date has been played and the crew goes home.
The result behaves more like a souvenir than like clothing, and souvenirs are bought on the strength of the evening rather than on any comparison with high street prices.
Online stores run on different economics
The same design sold through a web store avoids both the venue cut and the trucking, which is why the online price for an identical item is often noticeably lower.
What the web store adds instead is fulfilment, packaging, returns and postage, costs that scale with the number of orders rather than with the number of cities visited.
Printing on demand removes inventory risk altogether at a higher cost per unit, which is why online catalogues tend to be wider while the margin on each item is thinner.