Unfortunately any price system (like Capitalism - and all other social systems on planet earth to date) is not sustainable. That is because two things are required in a price system: constant growth and scarcity. If there is an abundance of something it cannot be charged for. So, we often take those things we have in abundance and burn them, dump them in the ocean, or even pay people to not produce. That's what keeps the price system afloat - scarcity abundance is not even an option (except for the privileged class).
There are many problems with the gift economy idea. Perhaps the biggest is that is does not take into account how to manage the massive amounts of technology that we rely on, and need to continue to utilize. Then there is human nature which includes greed and other maladies. Then there is the problem of organizing trades, which is largely limited to who you know and is enormously inefficient.
The best solution I've come across goes by the name of Technocracy. It is a technologically based and scientifically designed social system which has no money, but relies on an equitable distribution of goods based on energy units. This system utilizes all the best of our technological advances and can provide for true abundance for everyone in the system (probably an entire continent). It is a very developed and complex system presented originally in 1933, researched and developed by a group of engineers, scientists, economists, and others. Check it out in detail by visiting www.technocracy.org.
Capitalism? If we want to create a Utopia, which is a completely attainable goal, we're going to have to get off the exchange system and learn about the Gift Economy. Have you heard of it?
Okay, I'll bite. What exactly is the game of sabeve?
Earon