Here you go, this is untested, but you'll see if it works and if it not works, then I'll try to fix it. This only makes so when you hit the trigger, it will take 1000 points from you, but you asked for a buyable trigger so yea .
buyable() { buyable_trigger = getEnt("buyable_trigger","targetname"); player = getplayers(); cost = 1000;// change this for how much you want it to cost