Hmmmmmmmmmmm... Do you already have transmitters that put out 5W? If so, then they would be good candidates for this cheaper approach, get a 2M linear and modify it to the FM BC bands. Double the values of your capacitors and coils. Also, use fans and added heat sinking to take the heat of doing 100% duty cycle. One thing is for sure, watch what spurs you might transmit. Try to keep it as clean as possible, and don't park near an airport. These days the political landscape for FM pirating really sucks. I won't do it, but going mobile from one location to another is on way to try not to be a silent freq.