Your legally authorized low power radio station has excelllent programming but a disappointingly limited coverage area. You do not plan to run illegal power levels. But is it hopeless?
Take a look at the nighttime powers of local AM stations. Around the land there are stations with nighttime authorizations as low as 1 Watt.
It is unlikely that stations with extremely low nighttime power want to invest money in those hours and equally unlikely there can be a monetary return.
Step into the gap and lease the overnight air time and run your format at the, to you, higher power that you've dreamed about.
It might be a win-win.