I've wondered this myself at times.
The thing with structured education is that, particularly in science, there's core information that you really do need to know before you break into something as complicated as neuroscience. I suppose you could just sit down and teach yourself how neurons work, but it's important to understand the other basics because the body is a woven complex where one thing easily depends on the other. It's important to know the differences between hormones, neurotransmitters, neurohormones, etc. It's important to know what types there are and where in the body they act. It's important to understand basic chemistry, basic physiological functions, etc.
Now, I suppose we could all sit down and teach this to ourselves, but how do we know we're comprehending the information the proper way? Even in structured classrooms, students often digest the information incorrectly, and it must be corrected because science is just one of those complicated fields. This goes for any subject, really.
Should the option be there for those who want to self-teach? I guess so, but I guarantee that you'll skew your learning to something you're most interested in instead of, say, sitting yourself down and making yourself read Beowulf or a Spanish vocab chart or a history book.
There's also the idea that so much information out there is simply incorrect, especially on the Internet. And then, as what we want to learn becomes more specialized, such as neuroscience, we tend to need equipment and materials that become more expensive to maintain. Without a structured college system, I wouldn't have been able to study how cancer cells multiply and spread under a microscope, and I wouldn't have had the opportunity to learn how to work gel electrophoresis, etc. Especially with science, the materials simply become more expensive, and that's where we need to put in a lot of money. I agree that the knowledge and books should be cheaper, at least (my chemistry textbook was $450 this year, c'mon), but for higher education? I just don't know how possible it is to make research and lab experiments free for everyone.
Education is affordable for most. I go to a school that costs $60,000 a year, and that's just how much a lot of schools cost in America. But, I pay maybe 1-2k out of pocket. The school and government provide grants to me because my family income isn't as high as that of a brain surgeon and a lawyer. Even the most prestigious schools in the U.S., at least, try to make themselves as affordable as possible. Why don't we just lower the price in general? Well, I have no idea. Private schools must raise their tuition every year, which is a big problem here. Why? Who knows. America sucks.
I totally rambled, but whatever. You get me.