Great graphic on perfection vs. efficiency. Their questions to ask yourself are fantastic.
If you achieve perfection without any control of the expense, you will end up with waste. This takes you out of the green excellence zone. If you only focus on keeping your costs down without any focus on perfection, you will produce shoddy work.
Excellence comes from balancing efficiency with perfection. Basically it comes down to doing the best with what you are given. If you are given a million dollar budget for a project, the amount of perfection should reflect the large investment. If you are given $10,000 for a project, you should still be able to stay in the green zone by making the most efficient use of your resources as possible.