What details show the differences between the Bundrens and the Tulls, in terms of socio-economic class?

In As I Lay Dying William Faulkner tells the tragic story of the Bundren family’s quest to bury their mother. The Bundrens are a poor family in the rural South, and there are a few details from the book that denote their poverty. In contrast, their neighbors the Tulls are a wealthier family, they have means and run successful businesses, and are less neurotic—leaving them more time to be successful.
Faulkner begins showing the wealth of the Tulls and the poverty of the Bundrens in the first section of the novel, which is narrated by Darl Bundren. Darl tells us that he and Jewel his brother are traveling to their home in the first section. Jewel is described as,

...anyone watching us from the cottonhouse can see Jewel’s frayed and broken straw hat a full head above my own. (Section 1)

The state of Jewel’s hat is the first time we see that the Bundrens are poor. Jewel doesn’t have enough money to get a new hat, so he wears the one he has—even though it is broken. This image of him, wearing worn-out clothes, is contrasted with the image of Vernon Tull’s wagon,

Tull’s wagon stands beside the spring, hitched to the rail, the reins wrapped about the seat stanchion. In the wagon bed are two chairs. (Section 1)

The image of the broken and frayed hat, used beyond its life and the wagon with two chairs shows a contrast in the wealth and poverty of the two families.
The juxtaposition of the two families is taken to a new level when the Tulls remark about the Bundren's values.
Cora, when describing Jewel Bundren, remarks that,

“A Bundren through and through, loving nobody, caring for nothing except how to get something with the least amount of work.”

The Bundrens are characterized as a family that is ultimately selfish, cannot see beyond themselves and their problems, and that is tied to their lack of money. They will not work hard, and the task of taking their mother to Jefferson for burial seems strange because of their unwillingness to love one another.
Faulkner ultimately reveals that nearly everyone in the family is taking the dangerous and foolhardy trip for their own personal reasons, showing they are not just poor materially, but that their values are poor—social-class is tied to the concept of morality, the Bundrens lack many different kinds of wealth.