A tablespoon of gravy made with gravy granules is about 1½ syns.
Dissolve an oxo cube in a little water and use that, it's free.
A packet mix of white or parsley sauce etc made up with water is about 2½ points.
You could also make a sauce using Quark, which is free.
Check out the recipe section above, there will be some sauce recipe's there too.