Radio Jackie still do the car sticker game.
Yorkshire Coast Radio do one for £50 of fuel.
Jackie's is for £107.80. Not sure how that game is funded as it's a tiny station.
Often these promotions have a commercial sponsor which will more than offset the cost of prizes.
I understand the cost of printing car stickers has increased a lot over the last couple of decades, driven by the price of oil (a key raw ingredient) - one of the reasons why every radio station doesn’t have car stickers anymore.