If $40 to buy two is a lot of money, then $20 to buy one is also a lot of money (since, after all, it's the same price per unit), are you sure you can afford to

If $40 to buy two is a lot of money, then $20 to buy one is also a lot of money (since, after all, it's the same price per unit), are you sure you can afford to spend 50 cents/bag for garbage bags? We buy the big store brand box ($15 - $20 for 200). The box is a bit too big to put under the sink, so we put half in another smaller container under the sink. When we refill that container and the box is empty, then it's time to buy more.