You'd probably be surprised at how little time it takes. I think the current recommendation is around 4 hours/day. Some people eat 1/2 that just taking their kids to public school. By the time you've cut out all the distractions and extraneous stuff that goes into a regular school day, that's a good amount of time. I was surprised when I first heard about it but thinking back to my school days (a decent education. But I got lucky, the nearby community's school was a cesspool. Even then it took me a long time to shake the statist indoctrination) it is not really out of line.
My kids probably average around 3 hours a day, engaged in deliberate study of academic subjects. However, that's just about every day, including Saturdays and most of what most kids consider "summer vacation". They still complain about the amount of time that their studies (and chores) consume, right up until I threaten them with enrollment and a 7am bus ride. When they are really small, they think the bus is cool, so I occasionally take them on a public bus trip. (navigating the public transit system is a useful skill in it's own right) My younger kids are not really old enough for "school", at 4 & 5, and are so close together in size and age that most people assume that they are twins. They are my rough & tumble boys, and they fight like Cain & Able. There are a number of differing learning styles, and professional teachers have to learn techniques for hitting as many of them with each lesson as they can, in order to teach effectively to their entire class. This actually takes up as much class time as anything, and isn't something that can be avoided. But homeschooling allows the teaching parent to tailor the lesson to match the personality & learning style of the child. This is a huge time saver, and very effective once it's well implemented. What takes the most time is actual lesson planning, but I'm willing & able to spend the money to have that cognative labor performed by others, by buying curriculium developed for homeschooled children that fit their learning styles and our ideological parameters. Currently we use Sonlight for my older children. (sonlight.com) But one can homeschool a child well for free, using nothing but a library card and a little guidance from a website like this one...
http://www.oldfashionededucation.com/Or this one...
http://www.amblesideonline.org/And other online resources such as this one...
http://www.khanacademy.org/And this one...
http://ocw.mit.edu/courses/Money is a trade for time, in education as much as anything else. BTW, my kids have access to both Kahn Academy & MIT's Opencourseware via their Roku. The meatspace lecture model is a dying educational paradigm regardless of it's quality.