eBook sale landing page needed

Hi I need a good landing page designer to create good landing pages for the ebooks i want to sell. ebooks are for preparing to exams like GRE, GMAT, TOEFL etc. these are expensive exams and my target audience is ready to spend some money for an exam that will change their life and career. I will advertise on adwords, facebook and adcenter, selecting my target audience very carefully, so that it converts well. I will pay first half of money when the prototype is ready and i like it, and second half when after some test runs we do the needed tweaks to reach around 10% conversion rate.