I am not sure what part or if as in a whole you need to see something setup. I don't have that but i can offer what i would do to set this up. Also assuming this is a single player game.
Players gold would be the global variable. can modify it anytime in the game then.
The shop would multiple layers, in its own scene, where one side is players inventory (bottom interactive layer, just above the background stuff.) and then the other side the shop screen. Can use a book with pages or tabs to have the shop layers go visible or invisible. If you do tabs then every time a player clicks a tab first set all shop layers invisible and then the one they choose to visible, some headache avoided. Once you setup one shop layer it is copy and modify. The easy way of doing a shop is tab method with item picture and a buy button. Each button can be the same sprit, as with the item picture, but have a variable with the item name and price. then code will be somewhat like the following.
When player clicks on buy now
player gold = player gold - buy now price variable
add "buy now item variable" to player inventory.
When they do purchase something from the shop they click the buy button next to the picture and it deducts the gold and then adds it to their inventory. I do not know how you have your inventory setup that will be all you. You should have this setup first before you set up the shop and if so you should have some idea of how to add items to in in code. There are several different inventory how to's out there.