The expected cost and return a business sees from Google Ads varies based on industry, geographical region - and really is unique for every business. It's a hard projection to make. Our Google Ads Expectation by Industry file offers some projections based on industry - but keep in mind these are simply industry averages, and the best route is to run your ads for a couple of months, and learn from the results.
We find locally targeted, specific product/service categories (such as 'martial arts studio') see a low CPC average around $1, whereas highly-competitive industries (such as 'Financial Advisor') see a higher average CPC, up to $6.