I guess (in my slow cooker at least) I could scale it up to maybe enough for 6 people by just adding more of all the ingredients. If you like hot food, just add more chilli powder. I've used the same recipe with other meats. I use what's cheapest. It works out (with spuds and vegetables) about 2 to 3 quid a head. Use dried beans if you can. It means remembering to put them to soak the night before but they work out about half the price of canned beans.
For the pork, use the cheaper, fattier cuts found in your local butcher/supermarket. Instead of using 1 tin black-eyed beans, you could use kidney beans or dried beans soaked for 24 hours.