Most whites in the South didn't own slaves. Those who did own slaves owned very few. Those who owned dozens (or hundreds) were effectively the "1%" of the antebellum South. But slavery was more than a system of labor exploitation, it was a system of social control. Poor whites were equally invested in maintaining the slave system because the presence of African Americans generally and enslaved African Americans in particular meant there was always a social strata beneath them. Check out Keri Leigh Merrit's fantastic book Masterless Men: Poor Whites and Slavery in the Antebellum South.

As to your second question, white tradesmen complain about this all the time! In South Carolina, they write to the legislature to complain they are being undercut by free and enslaved black workers who "undertake the work for little more than the cost of materials." They accuse them of stealing materials to be able to do it so cheaply and say white people can't support family with those wages. White tradesmen decry African Americans monopoly on certain trades (barbering, carpentry, etc.) saying it disinclines whites from wanting to take on that kind of work. The chapter in my book on labor talks abut this a lot.