Given that the ACA forced insurance companies to sell insurance to people they previously found unprofitable to sell insurance to, basic economics suggests that the ACA probably raised the cost of insurance. That's not to say it makes it a bad thing. I would actually argue the opposite.

Also the ACA requires insurance companies to make a max gross margin of 20%. This looks like a cost saving measure at first glance, but it's actually the opposite. Now insurance profits are actually increased by an increase in medical costs, and therefore the insurance companies are disincentivized to control costs.