Total cost per ASM is probably at least $.13-.15 per ASM due to the poor economies of scale. LCC 737/A-320's run about $.075/ASM and CL-200 50 seat RJ's about $.11/ASM.
Conklin deDecker (Industry datasource) lists the DOC of a corporate 1900 at $665/Hr. (2003). DOC (Direct Operating Cost) includes fuel and maintenance. Add in about $150-200/hr. for reserves. An airline should beat this as they get bulk pricing on fuel, parts, and mx and tend to pay their employees peanuts. However, 121 compliance costs more than Part. 91 and is a major reason 1900's are disappearing from the airline scene. (Your government making the world safer by forcing millions of passenger miles onto the roads where one is over 100x more likely to die....)
You can search for a full Conklin report for purchase @ controller.com
With lots of 1900's getting parked the lease rates should be attractive.