For cheap lunch or dinner, I recommend Sesame. It's in the old section of North Charleston. They do burgers and beer mostly, but mostly everything is made from scratch, down to the ketchup and mayo. They grind their own meat, so you can have your burger cooked to your liking. They also have excellent bean burgers if that's your persuasion. Definitely get the sweet potato fries if you go. My personal favorites are the New Zealand Burger and the South Carolina Burger. But check out their specials---there's always something seasonal and one of a kind.
Here's the link to their menu: http://www.sesameburgersandbeer.com/V...
Hope you enjoy Charleston!