Health cost sharing groups are an alternative, but definitely not for everyone.
Health cost sharing groups typically fit under the ACA rules by operating as a ministry and using the religious exemption. That would require a specific religious affiliation or members.
The big ones I know of are Samaritan Ministries
, Christian Healthcare Ministries
(Ohio), and Medi-Share
(Florida). They generally require vows of abstinence (or the equivalent) from alcohol, tobacco, extra-marital sex, and 'debauchery'. There may be a need for members to chip in to directly assist others in need, in addition to monthly 'share' contributions, as a "Brother's Keeper" program.
There is a cap on benefits that one can receive per case. Samaritan Ministries cap is $250,000, for example, while another group caps at $125,000. Think carefully about those limits versus the cost of cancer treatment or major surgery.
Note that since these are NOT insurance companies, they are not regulated or reviewed as such, and are not subject to the same dispute resolution processes as insurance companies. Investigate carefully before using one of these services. There are scams out there, so please be careful.
Christian health-care sharing group offers alternative to ACA | CJOnline.com
Longer, more detailed analysis with citations: