For tax, go for Girish Ahuja along with module problems and practice manuals of icai. For Cost n FM also first refer module problems n practice manuals. Then do problems from suggested answers, RTPs, these are sufficient in my view. If you have time, then you can follow tulsian book for cost and fm subject. But the books are very lengthy.

costing- tulsian

tax- singhania or ahuja

cost: Module is enough

Tax: Paduka or girish Ahuja

FOR COSTING GO FOR PADHUKA AND FOR TAX GO FOR GIRISH AHUJA SIR BOOK....

Costing- padhuka

Tax - singhania

COSTING - P C TULSIAN (S CHAND & CO)

TAX - T N MANOHARAN (SNOWWHITE PUBLICATION)