The subsidies are available for households with income up to 400% of Alaska poverty line. For this year Alaska poverty line is the following amounts for the given household sizes;
Persons in family/household Poverty guideline
1 person $14,840
2 people $20,020
3 people $25,200
4 people $30,380
5 people $35,560
6 people $40,740
and so on. (from the Federal Register)

Of course, you multiply these household incomes by 4 to determine the subsidy cutoff. I don't qualify for a subsidy, by the way. But as you can see, these can be pretty decent incomes. Dermot's data appears to be correct. For further insight, I'd suggest following Dermot's link;
http://kff.org/interactive/tax-credits-under-the-affordable-care-act-vs-replacement-proposal-interactive-map/
It's pretty informative. I see three main reasons for our high AK insurance costs.
1) High AK medical costs.
2) The "Uninsurables" are now insured.
3) The "Invincibles" choose to pay the fairly trivial penalty instead of premiums.