Costs, outside the cost of extra testing for documentation, which are likely paid for by the institution, aren't likely to be exceptionally high. In round figures I estimate $200,000 to $250,000 but that is more a WAG. Not so high to avoid a death sentence. With time the prices would likely come down. Here again a lot depends on how much the various researchers, academic, medical, NIH, etcetera, are all willing to chip in.
Art, that seems probably not too far off. You might be a bit high, but I'm sure there are lots of misc. costs. A typical PICU bed runs $3-5k/day. Regular floor bed maybe something like $1k.
If they don't have insurance, I'm sure the hospital will work with them. First, it's UC-Davis, so a public hospital. Second, the article makes it sound like it was a collaborative effort between different agencies. While each one probably would charge, they also could potentially waive their fees. Third, it's bad P.R. Fourth, typically in cases like this the kid would be put on Medi-cal (Cali's version of medicaid) to help defray the cost a bit (if non-insured initially). And fifth... most hospitals are pretty reasonable about payment plans if you talk to them. They'd rather collect 20% of a bill than none of it.