The first thought that came to my mind is to use a battle end event. Generate a random base node and attach that to a "Add To Inventory". In that node insert a random amount of gold by using the quantity "random" selector.
When you add an Item Collector to a scene there is an option to add scripts or events into the Item Collector (treasure chest in this case). The same type of event would be useful in that situation because the box will have an inventory like a combatant. I don't know for sure what the event chain would look like in your example but it would be similar. The event system sounds like the easy way to change the values associated with items on the fly in your case.
The next update will make that easier, as quantity definitions in loot tables allow advanced value selections, e.g. using formulas or random values between 2 defind values.
For now, you could set up a loot table that e.g. has 3 potions set up, each with a chance like 50% to somewhat randomize the quantity you'll get. Another way would be setting up the potion with 1, 2 and 3 quantities and enable Get Random to only get one of the added items randomly.
Please consider rating/reviewing my products on the Asset Store (hopefully positively), as that helps tremendously with getting found. If you're enjoying my products, updates and support, please consider supporting me on patreon.com!
For now, you could set up a loot table that e.g. has 3 potions set up, each with a chance like 50% to somewhat randomize the quantity you'll get.
Another way would be setting up the potion with 1, 2 and 3 quantities and enable Get Random to only get one of the added items randomly.
If you're enjoying my products, updates and support, please consider supporting me on patreon.com!