I have not tried Dribble, but I have had experience hiring designers to help me with UI.
I went through trying to outsource overseas, to using Fiverr. None of this produced good results for me as most of the people I tried could not follow a specification.
I reached out to one of the main contributors of the open source SaSS framework I was using. He agreed to do the work for me for a fixed budget. He was a bit more expensive per hour than the other options, but I got exactly what I wanted. I did not have to go back and forth regarding my specification. If you value your time to market, I would recommend this route.