I'm not sure why you'd buy barbecue sauce, given that doing it yourself takes 15 minutes, has one basic pattern (ketchup/mustard + vinegar + seasonings), and avoids all the nasty aftertastes you get from store-bought ones.

This is my go-to recipe when I don't want to try something new, only slightly adopted from Virtual Weber Bullet forums:

Miss Piggy Mustard Sauce

1 cup generic yellow mustard
1/4 cup white sugar
1/4 cup light brown sugar
1/2 cup cider vinegar
2 tbsp. chili powder
1 tsp. Cayenne pepper
1 tsp. ground black pepper
1 tsp. white pepper
1 tbsp. dark soy sauce
2 tbsp. butter
 

Combine all ingredients except soy sauce and butter, adding vinegar last (to desired thickness). Simmer for 10 minutes, then remove from heat and add butter and soy sauce.

A couple of notes, for when you're making it your own:

  • I like to use Chipotle chili powder for a bit of a smokey taste, but try all the ones you can find to pick which one works for you.
  • Traditionally, white pepper is used to not discolour sauces - which clearly doesn't apply here. You could almost certainly just use more black pepper and not miss much, but the original recipe called for both (so I use both).

Despite this being a mustard-based sauce (traditionally from South Carolina), it'll end up looking almost as dark as a ketchup-based on - but you'll definitely taste the lack of a tomato base.