For free? Low, but not 0

You could consider using konoha great tree. Kakuzu and deidara were there for a really long time now and usually getting past their whole level gets you about 10 frags of each. Sure that requires more spending than 12 packs but its a good event in general when you use 19k on it. Also keep in mind those frags are addition and you still will be left with enough points to recruit pretty much whole most expensive ninja/summon in the rotation, as well as command flag/essence.