Hi Vijay
To estimate spraying costs you need to get "coverage" (m2/hr/0.1mm) and "powder required" (kg/m2/0.1mm) data for your specific powder and spray parameters. Failing that, deposit efficiency, spray rate and coating density can be used. From this and the surface area of the job and coating thickness desired you can estimate how much powder and time is required for spraying (allow a lttle extra for idle time, spraying off job etc.). From the time estimate you can then estimate things like consumption of labour, kerosine, oxygen, air, cooling water, electricity etc. Obviously, costing of associated process like cleaning, blasting, masking, sealing, finishing etc. are not included here.
Probably, not what you wanted, but I don't have the time or space to go into much detail. If you have any specific areas you are having trouble estimating, let us know. Your equipment manuals may have information regarding estimating costs.