If you are using 5 grains of powder per round then in theory you are getting 1400 rounds of finished ammo per pound. Multiply that number, in this example 1400, by the number of rounds you think you will shoot in a year. Suppose you think you are going to shoot 5000 rounds per year, divide 5000 by 1400 which means you might consume 3.6 pounds of powder. Round up to 4 pounds.
Then multiply 4 pounds by 4 (for 4 years supply) and make that amount your minimum powder purchase. So, you need to start this exercise with 16 pounds of powder.
When you get down to 8 pounds it's time to start looking for another 8 pound container. If it takes you a year to find it, in the case of a powder shortage, you can still continue to shoot without worry. If powder is in easy supply, as it is right now, just buy 4 pounds. You have now established a min/max system of stocking material. Your minimum amount of powder is 8 pounds, your maximum is 16.
If the total cost of powder is $35.00 (shipping, tax, hazmat and so on) and your using 5 grains per round, your cost per round is only 2.5 cents per round. Powder is the least expensive component for handloading.
Now is a great time to make sure you have enough powder to get you through the next few years of political uncertainty. Powder is easy, where it gets interesting and more expensive is with primers and then bullets. In comparison, powder is easy next to bullets. But bullets have been easier to locate than powder in times of high consumer demand, historically speaking.