SEO pay for performance project

I need to promote a plumbing website (name will be disclosed to the awarded freelancer). I need to rank in page 1 in google (organic) for at least 20 days for the following keywords:

plumber London
boiler repair London
emergency plumber London
London plumber
gas engineer London
heating repair London
plumber in London

I am willing to pay 40 GBP / keyword = 280 GBP for the entire project. Timeframe for achieving this - maximum 3 months.

After ranking 1st page in google for at least 20 days, I will release the payment for that particular keyword.