It seems to me that older kids would be able to understand a situation like this more easily, no? Of course, they are probably used to a certain standard by that age too.
One thing that works really well (we've done it on and off, but not consistently), is holding family meetings. At these meetings, you discuss issues and potential solutions. You write things down and don't disregard anyone's ideas. Let the kids talk. You (and the kids) can present the problem and they help determine the solution. When kids come up with their own solutions to problems, they feel like they have input and they are much more likely to follow through.
Get them involved in budgeting and family expenses. Let them see how much it costs to do various things.
When I was a kid, I played ringette, soccer, did track, figure skating, and gymnastics. It was crazy and probably cost my parents a lot of money. One year, they told me I could pick one winter sport and one summer sport and that was it. I picked gymnastics and soccer. Later, I learned that gymnastics alone was something like $300 per month. Had I known that, I would have understood more.
Also, it seems like kids are learning more about the environment and how to help these days. Saving money and not buying stuff often has a direct environmental or health benefit. Maybe presenting things from this side (with books and/or movies) might help as well.
Good luck!!