Next you can go but a pre-designed double garage plan but even though it'll come much cheaper that if you need a special design made you will most likely not be completely satisfied and especially not if you're looking to build a garage that will match your home. It is very unlikely that you'll find a garage that will fit the design of your house.
Finally you can contact a company that do garage plans for a living. If you find their prices to be higher than what you want to pay you can always go find an architect student and ask them whether they would be willing to design a double garage for you. Most of them will be short on cash as they're studying and they'll be more than willing to help you out. You do have to remember though that they are STUDENTS and not yet fully equipped to be an architect.
Check out this site for more information on garage plans.