Phil Heiple wanted a home solar electricity system to act as a power backup and to serve as portable power for vacations. But being a do-it-yourself kind of guy, he decided to assemble his own. This page lists exactly how he did it, at a cost less than $300 total.
It's worth noting that he didn't make a solar panel -- he bought one of those -- but a solar-charged power system. Whatever he needed to plug in actually pulled from the battery storage; the solar panel served to recharge the battery. In addition, the page appears to date from around 1996 -- and while the overall instructions are still quite valid, it would be interesting to see just how much better a system one could assemble for the same rough price with modern technology.
One of the more inspiring and useful sites to check out along these lines is Otherpower.com
They have more up-to-date examples of a similar spirit for DIY solar power. Plus excellent resources and discussions about other areas of renewable energy.