Options to change prices/rewardsSolved
Just had a few suggestions that I wanted to present to you. Have you thought about adding the ability to change prices and adding support for Server Rewards/Economics? 
Yes, I've certainly thought about it, and tried. However, the dialog UI is completely client side so it's not really possible to change the prices. I can change the server side code that enforces the prices, but the client will not show the option to pay if it doesn't have enough scrap. While it might be possible to trick the client by temporarily adding scrap to the inventory, the price amount showed client-side cannot be changed so the player would likely be confused.

The only way to properly display custom prices would be to make a custom GUI. I may add that later on, but it's a bit tedious to reimplement all of the dialog.
I was going to suggest this as well, but thanks for that explanation of how it works and why it's really difficult to implement. It's a shame since the prices for boats just make them not worth buying.
Hum.. Can you add only a simple text UI with the new prices over the dialog box part in order to hide vanilla wrong prices 🤔

I've done some work on this feature. You can download the beta with the following link.
https://umod.org/plugins/VehicleVendorOptions.cs?version=1.3.0&branch=beta

The config now looks like this:

{
  "Vehicles": {
    "Minicopter": {
      "FuelAmount": 100,
      "ScrapCost": -1
    },
    "ScrapTransport": {
      "FuelAmount": 100,
      "ScrapCost": -1
    },
    "Rowboat": {
      "FuelAmount": 50,
      "ScrapCost": -1
    },
    "RHIB": {
      "FuelAmount": 50,
      "ScrapCost": -1
    }
  }
}​

The ScrapCost option is a global setting for all players. Setting to -1 (default) uses vanilla prices, so as to avoid server owners unintentionally locking in the prices, as they may want to follow the prices that the game developers set which could change.

Next, I'll work on adding support for Server Rewards and Economics, as well as multiple prices. Will probably need to include custom UI alongside that or it will likely be confusing to players.

Is having multiple prices something people would be interested in? For example, we could design the config like this:

"Minicopter": {
  "FuelAmount": 100,
  "AlternatePrices": [
    {
      "Item": "scrap",
      "Amount": 100
    },
    {
      "Item": "scrap",
      "Amount": 200
    },
    {
      "Economics": true,
      "Amount": 100
    },
    {
      "ServerRewards": true,
      "Amount": 100
    }
  ]
}

This would then automatically generate permissions like the following.

  • vehiclevendoroptions.price.minicopter.scrap.100
  • vehiclevendoroptions.price.minicopter.scrap.200
  • vehiclevendoroptions.price.minicopter.economics.100
  • vehiclevendoroptions.price.minicopter.serverrewards.100

I've released v1.3.0 which supports custom scrap amounts, other items, Economics, and Server Rewards. There is also a lightweight UI label that is floated on the conversation box when the vanilla price doesn't match the vanilla one, so that the player can be informed.

Locked automatically