In some states the necessary ID is free, but "free" just means that there is no fee for the ID or to apply for it. It does not mean that getting copies of the necessary documents that must be submitted with the application are free. Those can sometimes run to over $100.
Here's a collection of links I've saved over the years on this:
https://www.projectvote.org/wp-content/uploads/2015/06/AMERI...
https://www.politifact.com/factchecks/2012/jul/11/eric-holde...
https://www.aclu.org/documents/oppose-voter-id-legislation-f...
https://www.usccr.gov/files/pubs/2018/Minority_Voting_Access...
https://www.washingtonpost.com/politics/courts_law/getting-a...
https://www.vox.com/xpress/2014/11/4/7157037/us-voter-id-req...
https://www.npr.org/2018/09/07/644648955/for-older-voters-ge...
https://rewirenewsgroup.com/2014/10/16/well-actually-pretty-...
https://www.theregreview.org/2019/01/08/shapiro-moran-burden...
https://www.theatlantic.com/politics/archive/2014/10/heres-h...
https://scholars.org/contribution/high-cost-free-photo-voter...
https://now.tufts.edu/2018/01/23/proving-voter-id-laws-discr...
https://www.brennancenter.org/our-work/analysis-opinion/debu...