I can build a 250W output amp using a 4X150A for 222 MHz for about $600 or so. So can you, actually! It's not difficult with basic tooling and soldering skills. Using transistors might be slightly more expensive since it would involve a more complex power supply to convert 120VAC to lower voltage regulated DC. My dual 4X150A amp started out life as an FAA transmitter, I just converted it to 222 MHz and added a homebrew power supply since the original one weighed about 200 lbs and that was silly. I published some construction articles in 73 magazine on this stuff in the early 90's, it's all on line at archives.org However, that doesn't answer the "mobile amp" question at all. For a mobile amp, Mirage may be just about the only thing on the U.S. market right now. 222 MHz is only an amateur band here in the Americas, so the market is very limited. I'm impressed the Japanese/Chinese even make anything for this band, as their "local" market is nonexistent.