I don't dive rebreathers, but have enjoyed reading about them. I dive regular scuba, on air. I also dive solo. So I keep it simple, and many times also dive vintage equipment I service myself. I also have been diving for over 50 years now.
But let me venture that all you say above is true, that insurance, supply and demand all factor into the expense. But something else does too, which has not been mentioned--product safety evaluation is also very important. Many of these systems use sophisticated computerized systems to sense oxygen levels, and add the inert ingredients (sometimes two of them, nitrogen and helium for instance). You would not want to use a system which had not been thoroughly tested, and this is a major expense.
When I bring an old double hose regulator back to life after forty years of non-use, I first take it to the pool to "qualify" it for open water. Sometimes, it doesn't make the grade, such as the DA Aqualung regulator which breaths hard enough that in a fast-moving river it could become quite a liability. At other times, I find a regulator works well both in the pool and the open water, such as the Mossback Mk III (a first stage modification for an U.S. Divers Company Aquamaster regulator).
When these rebreather manufacturers bring a new product to life, they are betting their company, and your life, that they have "qualified" this life safety apparatus to work under its design conditions every time it is used. This is why I won't even consider trying to design something like this myself. I don't have the expertise to design and test such a system. You need to understand this aspect of it too.
SeaRat