As A Procurement Contracting Officer working on a $50M service contract for aircraft maintenance and restoration.

Please help if you can.

As A Procurement Contracting Officer working on a $50M service contract for aircraft maintenance and restoration.  If the is no agreed rates between the contractor and the Government. But report indicated that there are Government recommended rates which differ from rates that the contractor proposed.What rates should be use when developing your minimum, objective, and maximum positions? 

Who would be contacted to aid you if necessary? 

How to justify it to the contractor during negotiations?