This is one issue that the (usually upper middle class or better) car-free advocates completely ignore that really ticks me off. I don't want people who don't have much money to have to choose between spending that money somewhere local but overpriced and taking a bus across town to go somewhere that actually gives them a good value.
I grew up somewhere that is almost an island and when there's little competition (everyone has to choose between the same few local options) all the businesses turn into rent-seeking scumbags. I remember when we used to leave that dump to visit relatives we'd always do our shopping on the way back because the non-local supermarkets were cheaper. When I go visit my parents I still ask if they want me to bring anything from Walmart.