Personly I go to the vender and buy 20-25 (200cr) rank 1 and 20-25 (600cr) rank 2 of thier fav one (96 gain 1 0-1999, rank 2 2000-3999 then only 1/2). For 20,000cr you get your npc up to 4k affection and also have a few mission for them to do that can get you maby another 1k. If you see then in the GN you can even do it for less. Mind you this will take you about 25-30 min to give them all of these though.