Your PPC costs can be calculated based on your audience and ad quality. The amount of money you want to spend for a user to click on your ad is called your bid. You enter your bid into an ad auction and the highest bidder gets it. Therefore, the more competitive you want to target, the higher the costs will be. Moreover, Google also monitors the quality of your ads so, if your ad quality is high, you can maintain lower costs as Google will rank your ad ahead of competitors. Understand all these factors, and then you can define your PPC budget.