grrr sorry i didnt see your message. not always signed into Umod. 

My idea is to allow players who dont have permissions to be able to buy "backup" as such 

You can literally still do that with Server Rewards as a Command Purchase and would look something like this, of course customize it to your likings. This is how I have it set up on my servers, adding this to the last entry on the reward_data.json file for Server Rewards.

"Callin Paratroopers to your Locations": {
      "description": "Calls in a Paratrooper Event on your position",
      "iconName": "https://assets.umod.org/images/icons/plugin/5b6770996ef0d.jpg",
      "commands": [
        "say <color=#0099CC>$player.name</color> has called in a Paratrooper Event to their location",
        "pt player $player.name"
      ],
      "displayName": "Call Paratroopers",
      "cost": 7500,
      "cooldown": 43600
    }

Hey buddy

So when i use ur example for Server Rewards it cannot locate the player :(

05-18 20:58:54 | [Paratroopers] Could not locate the specified player