Is it necessary to insert the energy cost to LEED simulations ?

I'm doing a simulation for LEED and I already read the Appendix G of ASHRAE 90.1. It did not seem necessary to perform an energy cost analysis in the simulation, only an energy consumption analysis. However, reading the regulation of LEED, I see that it requests this cost analysis in the simulation.

Then I ask:

1) Is it really necessary a cost analysis between the baseline and the proposed model in a simulation to be submitted to the USGBC?

2) Is it possible enter the full energy cost data in OpenStudio? If so, how?

To answer your first question YES.

It is a requirement of ASHRAE Standard 90.1 Appendix G to determine the annual costs of both the proposed design and baseline design. Section G1.2 of ASHRAE Standard 90.1 require calculating the percentage improvement using two defined terms "baseline building performance" and "proposed building performance". These terms are defined in Section 3.2 (of 90.1-2007 but I believe it essentially the same in other versions) as "the annual energy cost for a building design intended for use as a baseline for rating above standard design" and "the annual energy cost calculated for a proposed building" respectively.

As for your second question, I believe that you can enter energy cost data in OpenStudio but I will defer to someone else to tell you how to do that.