For Costing - You can refer Saxena and Vashishth. But For MAFA , I will suggest you to take question bank with solution od any teacher who takes MAFA classes like Ashish Kalra or Rajesh Makkar for practise. And theory part should be covered from ICAI Study material itself. I also have studied self in the same way. For practise some question bank is necessary. But still if you want to go for some book, then Khan and Jain can be a good option for you.