i dont know about costing part of tulsian. so i cant suggest u about that.
one thing i would like to tell u is that u can refer any book (for concept and practice) but u must cover pm question coz most of questions are of same pattern as given in pm, sm .
Regarding O.R. , i would suggest tulsian book.In addition to that i have found some lectures on youtube about o.r. those wr really helpful. So u can also go for it else book is sufficient for good concepts.