Two write-ups from real campaigns. Both name the budget, both show the working, and both say what the numbers cannot tell you, which is the part most case studies leave out.
47 leads from $179 of Meta ad spend on a lead-form campaign for home tours, roughly 4× below the published real-estate median. The full arithmetic, including what the conversion rate did.
$11,113 in sales at a 4.08% conversion rate for a small Shopify store, with two thirds of revenue traced to an Instagram audience built without ad spend.
Both name the actual budget, not a range. Both show the arithmetic, so you can check it. Both are campaigns run end to end rather than a slice credited after the fact, and both say plainly what the numbers cannot tell you: the real-estate one was a small spend over a short window, and the Instagram one took two years of posting nobody paid for.
What you will not find is a logo wall, an unattributed percentage, or a result with the spend removed. If a number here matters to your decision, the write-up shows where it came from.
Both predate Kerr & Company. They are here because the method is the one still used, not because the brands are impressive.
Tell me the business and what a new customer is worth. I'll tell you what I'd try first, what it would cost, and what the numbers would and would not be able to tell you.