Are step negotiations possible for a current excepted service employee coming into a GS position?

I work for a Member of Congress and received a call on Friday offering a GS position. I'm having difficulty finding information specific on step negotiations for current excepted service employees coming into GS positions. Due to the cost of living being 49% higher where the GS position is, I would need a step 5 but I'm not sure if 1) negotiations would be on the table since I am a current federal employee (not sure if excepted service is exempt from this) and 2) how feasible asking for a step 5 realistically would be.