Google Adwords management for media company

We have an ongoing Ad Words campaign. It is run by third party company. We are unhappy with their performance and looking for a replacement. We need a freelancer who will look at our existing campaign, analyze it and tell us whether he can improve it : CPA and number of conversions. What budget he will need, based on prior history. Chosen freelancer will run the campaign month to month, will be analyzing and improving, creating new ads