Summary: Translating well is very, very hard. Most translations are poor. Good translations are usually very expensive.
You will get what you pay for, with some margin of error. If someone is cheap, I most strongly recommend you do some additional work getting the results checked. Make sure you have a method of evaluating the translations.
We assess the quality required, then use professional translators in the appropriate prices range. Poor translations will noticeably affect your users' perceptions of your product.
And no, I don't think there is a happy meduim you've missed. I would also advise you to be careful using the Mechanical Turk without an independent method of assessing the result.
Sorry to be so negative, but we've had some bad experiences through over-optimism. Learn caution from our mistakes.