They don't exist. You "might" be able to find a half-decent diaper at medical supply stores, but even then they aren't that good and will leak on you overnight (based on your other posts). At best, they are only ok enough to "get you through" till you can get something better. Store bought diapers aren't a good price either. They may look inexpensive at first, but when you add in all the extra changes needed that just multiplies on to your overall cost per day.
The absolute cheapest diaper I have ever found is Betterdry. With just 1 diaper per day I only spend a little over $1.50. (Though I typically use 2 to avoid rashes and smells). No store bought diaper can come anywhere near as close to that. And as a bonus, I find Betterdry to be extremely reliable and almost never leak on me. PeekABU is an extremely close second to that. And "in a pinch" I find Confidry24/7 and Northshore Supreme to be a tie for third best.
Give each of them a try and see if they work for you too. Remember though, total cost per day. Not price per diaper.