Solar is only becoming cheaper today because of the research and capital that was put into developing the technology, not because it's inherently cleaner than coal. To your point, based purely on the market forces (i.e. excluding carbon taxes) coal is still a very viable option. And if the government is motivated to migrate businesses off of dirty energy resources, it also has a motivation to help develop alternatives that the market will accept.
Solyndra[0] was one example of a company that received government support to develop solar technology and became notorious for defrauding the government in the process.