Ridiculous gas prices

Okay, I am so infuriated right now with Missouri's ridiculous gas prices. I understand that the nature of gas prices is to fluctuate. I'm okay with it ticking up and down a few cents every day. That is totally fine. What I am not okay with is what happens out here. Maybe it's just St Louis. I don't know. But Here's my story.
Wednesday night I went to Young Women's. It's about 20 minutes away. On the way home, I saw that I had about a quarter tank left and I knew I had playdate the next day. What I didn't have was any money. So I thought "well, I will just leave early tomorrow and get gas before we drive up to Troy." Troy is about 30 miles away from us. Gas price in Warrenton on Weds night: $3.35 a gallon.
Thursday does not go as planned. I wanted to leave at 9 and we didn't get out until 9:20 and I was supposed to be in Troy at 10am and Claire had got potty at 9 and wasn't wearing a pull-up and I didn't want her to pee in the car. We were going swimming, so when she asked not to put it back on under her swimsuit, I agreed. So I skipped getting gas on the way out of town. Price in Warrenton at 9am: $3.35. (A note about the gas stations in warrenton- from my house going north there is one all by itself which is usually last to change prices, than a cluster of 4  on one side of the highway and another 3 or so on the other side of the highway. The ones in town always change at the same time.)
On the way to Troy, we pass through Hawk Point (town of 300 or so). Price in Hawk Point- $3.42. We get to Troy. Price in Troy: $3.49. I'm thinking, ouch. That's a whole 14 cents higher than home. So we go to playdate and the kids have fun and we leave around noon. The kids are tired from swimming and hot and cranky and hungry. So we go to McDonald's for some chicky fries. They had people outside taking money and handing out drinks and it was very distracting. We get right on the road to go home and I completely forget about getting gas. When we pass through Hawk Point again, the gas light comes on. I don't often drive to the gas light on this car. I did it a lot in the Matrix. But this one has a Distance to Empty Calculation that I check if I think I am getting low. (That and I've been trying to fill up at half tank just because you never know what will happen when you live so far from town.) The one other time I drove until the light came on, I checked the DTE readout and it said just a few miles, so I stopped and filled up and sure enough put 22 gallons in it. So that scared me into thinking that the DTE was pretty correct. No margin for error there. I quickly analyze the situation. 16 miles to Warrenton where I know gas is at least 8 cents cheaper. (22 gallon tank remember, it adds up quickly.) DTE is 12 miles. I know that there is a LOT of downhill to cover. The kids are tired and still fussing at me. Options- chance it. Alann is home and could come rescue me if needed. Stop the car- children explode from fussiness. I choose to chance it. I drive the 16 miles totally stressed out. I'm checking the DTE constantly, pulling out every fuel saving trick I know. I coast down every hill I can. I got a lot slower than normal. I make it to the church (which is north of town)  and breathe a little easier. Town isn't much farther. I get to town. Price in Warrenton at noon- $3.57!!!! Yes. $3.57. 22 cents more expensive than when I left 3 hours ago. I hope against hope that the stations across the freeway haven't changed yet. No luck. Okay, new choice to make- try to get to the one lone station that is about 2 miles down the road and past 4 stoplights and may still be cheaper, or fill up here. DTE reads 0. Zero miles to empty. Remember, last time, it was quite correct. So I bite the bullet and fill up. I briefly consider only getting a few gallons and going to Casey's, but the idea of making ANOTHER stop is not good. The minute the car stops moving, the kids freak out. They aren't hungry anymore, but they are tired and cranky and get upset when Elmo stops. So I fill up completely. And only put 20 gallons in the tank. Excuse me? I had TWO gallons left. That's 50 miles, on a bad day. I could have easily made it to Casey's. So I'm a little upset. We drive past Casey's and it's still $3.35. Ouch. I paid an extra $5.
Friday (today) we went to the Temple. Gas price in Warrenton: $3.48.
It wouldn't be so bad if this was a one-time occurrence. Okay, maybe they spiked the prices because it's Labor Day and they hope people will be filling up on Thursday to "beat the rush". But no. This happens ALL THE TIME! Gas prices jump 20-30 cents and then over the next 3 days or so fall back to the original, and sometimes lower. It is SO frustrating. Alann usually tells me when he drives to St Charles what the gas prices were because that will somewhat predict our prices. And like I said, I try to fill up when I'm at half tank and it's in a low peak. It's just so irritating. It really makes me mad. It's just not right that it should fluctuate that much that quickly. It's not nice. And now I don't know if I should trust my DTE or not.