Combine all ingredients (except toppings) in the slow cooker or a large pot.
If using the slow cooker, cook on low for about 90 minutes, or until the soup is hot. If cooking on the stovetop, bring the soup to a boil, then reduce to a simmer and cook covered for about 90 minutes or until the soup is hot. On the stovetop, stir occasionally.
Top each portion with sour cream, shredded cheese, and tortilla strips.
The cost estimate of $20 ($2/serving) assumes purchasing prepared pulled pork BBQ rather than using leftovers. Using leftovers brings the cost closer to $1.25/serving.