[tjohns]

That's a complicated topic, but the short version is cost of this treatment needs to cover the R&D costs to develop it, plus the costs for all the other failed experiments that didn't work out.

Plus gene therapy is in its infancy, so everything here is going to be novel and expensive. Novel treatments generally have a limited audience with even fewer practitioners, so you can't spread the R&D costs across many patients.

Prices will go down with time as patents expire and competitors emerge and this line of treatment (perhaps) becomes mainline, but that's on a ~20 year timeframe.