First, we set the criteria as basically two non-smoking adults with two kids in Utah making a total of $45k/year.
So, the hypothetical family above would pay $221/mo ($2,650/12) for the Silver plan with the out-of-pocket maximum at $4500 and free preventive care. Here's an example Silver plan looks like with Altius. See healthcare.gov for a selection of plans.
$221/mo for solid health insurance for a family of four making $45k/yr? Looks like the ACA is set to benefit a large swath of the middle class. And good for them!
Postscript: To be more clear, this calculation is done assuming the family can't get insurance through an employer. To be even more clear, and for those who aren't aware, without the ACA a private health plan would cost substantially more than ~$221/mo.