I-77 North between Charlotte and I-81
If you want something good, cheap, and some of the best authentic mexican tacqueria food around, there's a market/tacqueria across from the Burger King in Elkin, which is right off I-77. They press their tacos to order and their sandwiches are amazing. I recommend the cubana(which is more like the mexicana)or the pastor sandwich.
1401 North Bridge Street, Elkin, NC 28621 (across from burger king)