The price really depends on the construction of the building (concrete block or steel panel), its condition and the method of application you will use.
A steel building in good shape is easy to do but a concrete block building needing block fill primer before painting is more costly.
Ask yourself; how much material is needed (Include Everything!) and how long will it take me. Price out the material and equipment and give yourself a good wage. Add these together then multiply by 10-15% for a decent profit margin. For a better or closer number go to your local paint store and ask what the going "Good" wage is for a painter in your area and also price out all material while your are there.