Quick google search says UL certification costs about $5-$15k. I am assuming the product development will cost much more than this. Obviously this is an idea requiring investors (or grants) and a team of engineers, automation experts, computer systems, etc... I am wanting to gather that team now, and will need a few people who are well versed in RMH technology.
Matt Walker at Walker stoves sells kits. Dragon heater may be selling kits.
Any kit sold would need large amounts of local materials.
Your average home owner is not likely to have this skill level.
You would need certified builders and your cost would rise to the level of masonry heaters.
I think your estimated cost of UL certification, is low.
When it comes to open flames , they get very serious.
Safety from flames / sparks and safety from CO gasses indoors would be of paramount concern.
Masonry heaters are certified , but only if built by a certified mason.
They must be built with a complete double skin to ensure they will not be hazardous to people or their homes.
Cost is well above what most folks are willing to pay.
After all why deal with wood burning (yuck, dirty) when that nifty wall thermostat goes up to 80 F ?