When buying prestige points the rules say you can only execute the action once per turn, but when you do execute it can you buy as many as you can afford, or just 1 "transaction". For example, if the exchange rate is 1 to 3 can you just spend 1 gold to buy 3 points, or say if you had 3 gold could you spend all 3 to buy 9 points?
One transaction. So if it is 1 to 3, you can only spend 1 gold an no more.
Some cards let you do this twice.