Don't Just Look at the Initial Cost
Looking at only the initial cost and ignoring the operating costs causes you to make bad decisions, because over the lifetime of a house, the operating costs far outweigh the initial cost. Of course energy is an increasing cost, but maintenance is an overlooked, and often underestimated cost. Remodeling a bathroom can easily cost $10,000 and a kitchen can easily cost $30,000; a new roof is maybe $5,000 and having your house painted is at least $10,000. Since a lot of the cost of a house is labor, by putting in cheaper, less durable materials your actually costing yourself money in the long term.
Some things, like added insulation cost very little, even if you have to build thicker walls to do it. Often you can recoup some or all of this cost immediately by downsizing your furnace. Energy efficient appliances often have reasonably short paybacks periods. Some things, like passive solar cost only a little extra design time.
Of course, everyone has a budget, and there is a limit to how much up-front cost you can afford. When it comes to deciding what to buy or built, our philosophy is to get the most beautiful house you can afford, not the biggest. We'd rather live in a well built, beautiful cottage then one of those suburban behemoths with acres of granite counter tops.
Every year, more environmentally friendly materials appear, and every year they also get cheaper. In most cases it is possible to build in a significantly more environmental way for a 5-10% additional up front cost, and some things can be done for no additional cost, or even a savings.