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Using the API is a create an support solution.
The API is a great way to automate many processes; or tie your internal data to your AdWords account; however, for a small spend - it might not be worth the overall cost of implementation and support.
The API does have some costs associated with it beyond what you would pay a developer: [code.google.com...] however, the trick with the costs is to write efficient code. There are many ways to accomplish the exact same operations with the API, and while one way could be expensive - another could be cheap - hence, it is worthwhile working with someone who is familiar with the API and your goals.