If you don't mind, I'd like like to go into a little more detail about I'd like it to work.
Shop, Display
Place the shop at spawn, with the traders being villagers. The villagers name could be what they are buying + the price, ie 'Sand - $5'. These villagers are placed in clear view of all, but behind glass, so that people can determine whether or not it is worth it the buy the ticket. Also, make the ticket price 10-20%, maybe even 40% of the players bal. Scratch that, thats not going to work.
Ticket
Buying the ticket, you right click on a sign saying 'Buy Access' or something, but due to the exorbitant price it will say in chat 'Are you sure you want to buy a ticket? Say no/yes' this will prevent people from accidentally buying a rather expensive thing. Also, the ticket will be a piece of paper named 'Trade Access Ticket' or some such, and it will have the Lore 'Valid only for ', as though this will require a bit of coding it will prevent thefts.
Selling
Selling itself requires the player the right-click the Trader to sell 1 item, left click to sell a stack, and (maybe) shift right click to sell all they have of the item in their inventory.
These are just some suggestions, but I feel it would make it easier to use/navigate.