I would recommend you get a dedicted designer for the following reasons:
1. a professional will listen to you and create something that has your input. It may take hours, even days and you have a right to reject mediocre ideas. A professional should give you at least three options to choose from.
2. a design that has both your input and the professional is likely to be original and unique, unlike something you might pick on the web.
3. you can move to copyright your design against infringement, something you cannot do for designs that may be available to everybody else on the web.
4. your final product, when it finally meets your expectations and you have paid the designer for it, will give you endless years of satisfaction especially after it is well established in your corporate identity.
It will definitely cost more to get your logo from a professional but it will be worth it in the end.