Recommended way to pay for PPC based on Performance?

Hi
We are looking to find people that we can pay to set up our adwords accounts and pay them based on performance of the account..
The idea of paying a percentage of our spend does not incentive someone to keep our costs low and results high.
Does anyone have any suggestions for this?..
We are looking at a very large account with many keywords, landing pages and a monthly spend of £10,000.

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