My husband and I work opposing days and hours to keep our kids out of daycare (which also means they go wherever we go, all the time). It's a boatload of fun grocery shopping for a family of 5 with 3 kids in tow. I've done it at midnight just so I didn't have to bring the babies with me.
But to do it in an economy-sized car? No thanks. I'll pay the extra right now, because until I'm out of the carseat/booster seat phase, smaller won't work.
Then I'll repeat what I said in #37; when you decided to have a large family, you made a decision to incur certain expenses, and gasoline is by no means the largest of them. That was a decision you made willingly, and I'm sure you knew it wouldn't be cheap.