As for eco-friendly pre-fab homes, I know a little bit, but not too much, about them. The person who does know is a guy named Minh Pham, in suburban Maryland. He has an interesting story. His family came to the U.S. from Vietnam as boat people. They worked their way up and by the 1990s Mihn had a business degree (I think from the University of Maryland) and had gone into financial planning. He moved from that to being a real estate investor, starting with lease-options. He then moved into coaching other real estate investors. More recently, he's moved more into the whole life coaching and life simplification area. But one of his areas of particular interest has been low-cost, eco-friendly housing. Minh's website is http://walkingonwater.ning.com/ If you're serious, you have to talk to him. (Note: I've obviously met Minh a number of times over the years and have gone to a couple of his seminars. But I'm not receiving any compensation or benefit from the referral. It's just that it sounds as if he's the right guy for you to talk to.)
Hope that helps.
As to the cost - there are a number of websites, and the magazine "dwell" might be a helpful resource.
Give me a call to discuss further.