I understand that you want it so you have to pay them to avoi being attacked. If you do what I told you it will play out like this:
A player enters "-Bribe Red" (or whatever you want it to say, maybe -Ally Red) as a chat string
A dialog appears for the triggering player. Asking if they want to pay red to keep them from being attacked by red.
If they click the "yes" button, it will check if they have the right amount of gold and if they do, deduct the gold from their current gold and add it to reds and then change them to allied without vision with red, or with vision if you want, if they don't.. then just send them a message saying they don't have enough gold.
If they click "No" then do nothing, or you could just have a yes/ok option.
Also don't forget to add into the yes option to check if they are already an ally with red or not. No sense in paying for nothing..
If you need me to make an example trigger, just say something.