The bill nobody shows you
You get quoted for a website. You pay. The website exists. End of story. Except it isn't: that website needs five things to stay alive next year, and four of them get charged to a card.
This isn't a knock on the model. It's just the reality of having something connected to the internet 24/7. A car doesn't stop costing money when you drive it off the lot, and a website doesn't either. The difference is that your car gets an inspection reminder; your website tells you it's down when a customer says "your page isn't loading".