The average cost for an ACA premium in 2015 was $374 per month, but since 85 percent of people signing up receive a subsidy the cost is actually much lower.

"Among consumers who are signed up for 2015 coverage to date in the 37 HealthCare.gov states, 8 in 10 could choose a plan with a premium of $100 or less after tax credits, based on available options."[1]

[1]http://www.hhs.gov/about/news/2015/02/09/almost-6-point-5-mi...