I can educate both my children to a higher standard in a far more personalized education form for less than $5,000 per child per year in actual financial cost. This includes progressive curriculum materials, paid external learning opportunities (things like park/nature center passes, museums, group activities, etc.), travel costs (yes, we actually do a far amount of local and some longer travel in the course of their school year for education purposes), and school supplies.
Opportunity cost tends to be more subjective and harder to realize because the success of opportunity is hard to predict. Does that mean I live in a single-income household? Yes, but my spouse and I chose this because we wanted to give our children as good an opportunity to succeed as we can and this was the way we were determined to do it. My spouse is actually has a higher education level than I do but chose to stay home and do this for our children. My spouse doesn't see this as the loss of opportunity but the gain of ability to spend more time with our children helping them learn and grow into compassionate, driven, and hard-working individuals. The fact that we can do so for less actual cost than the public or private school systems is just a bonus.
(I do realize this is anecdotal, but it is the best source I have right now and other homeschool parents in my area say much the same regardless of ethnic or economic background.)