You can already choose what transactions you want to include by manually setting up NPCs with the function commands you want (not using dialogue commands). You can also only set up custom shop NPCs instead of the other shops.

Due to the way functions are programmed in the game I can't add a feature that lets you dynamicly set prices for functions as that's hardcoded in the function file, the custom shop works by using dynamic properties and the JavaScript api. You can also always edit the function files yourself if you want to rebalance every file, and also reflect these changes in the dialogue files if you wish, but there are some prices that I agree can be adjusted in a upcoming update.

Thanks for the feedback and info about the help dialogue. I have version 1.10 1 installed right now but the help menu is opening fine for me . If you're using an NPC make sure to update it as I changed a lot of the help menu in 1.10.0 (even if you're using the help npc from the setup function as I forgot to update that but it's already fixed for the next update 😅), and to access the admin help you need the moneyzAdmin tag

For the custom shop if you go to the Admin Menu > Manage Properties > Manage Shop Properties you'll be able to select an existing shop property if any existing or add a new one. The property name must follow this naming scheme: shopItem_unique-identifier (for example shopItem_moneyzMenu)

For item name enter the name of the item. You can find this from the /give command. (I don't think vanilla Minecraft items need the minecraft: name in front of it, but for custom items it'll need to be for example zvortex:moneyz_menu)

For buy amount enter any number you want the item quantity of (5 for 5 sticks for example)
For Buy cost this is the cost of them purchase
For buy data this is usually 0 unless the item has variants like dyes/whools

The same applies for the sell fields

Let me know what you've tried/don't understand, and I'll be sure to add it in the help menu