I just got an accepted offer on my first property (!) but already there's a curve ball thrown at me...

The occupancy inspector office will require that we add a full staircase, either wooden or metal, from the 3rd floor of a brick 3-unit in south STL.  I'm wondering if anyone has experience adding a fire escape to a similar property in St Louis?  I have 2 quotes - one for $6k and another for $40k, so hard to get a beat on it from that alone.  This is purely to meet code, so small landing platforms, cheap materials...just utilitarian in nature.  

Creative solutions or referrals are welcome.  Thanks BP!