Setting contextual advertising

There is a website for the sale of law books

Attendance small, but the sales are consistently 5-7 customers per day. I would like more. And on this, I want to start a contextual advertising in Yandex or Google (preferable Yandex).

Send answers: Coca advertising budget required for the test? how much per month do you need for a effective company? how much for the setup, launch, support? Is it possible to calculate in advance the result?

If you have successful work (cases) - I would like to see - it certainly will be a plus.