Our singer needs to be LOUDER!!! he was singing raining blood and we could barely hear him because he was only singing through a 15 watt guitar practise amp with a 6 inch speaker

. We are playing with drums that have full on double bass, my 180watt bass amp through 15"cab and a Roland cube 60 (which is surprisingly not that loud).
Anyways the loudest thing are drums we just need the singer to be able to sing over that, what would be the minimum power and speaker size needed for this?
BTW we are going used here as funds aren't much, so we are going to be looking at, keyboard, guitar and bass combos, anything that is loud enough and affordable.