The individual who wants to develop a personal blog will want the cost to be as near to zero as possible as there is no income generated. They may be prepared to spend a limited amount of money, but purely for vanity reasons.
The individual who wants to generate some money will be prepared to spend a little on themes and plugins in the hope that any outlay is recouped from the money earned. The more experienced a user is the more likely they are to pay more for a specific theme or plugin that increases their chance of making money.
The company in need of a website will have to weigh up the cost of a custom coded website VS a WordPress website. Sometimes, a WordPress site just won’t do the job. ( For example, it may need to integrate with certain software, deliver certain types of content, perform certain tasks, etc.) But assuming WordPress can do what the company wants, the company will be prepared to spend a little bit more on the themes and plugins knowing that it is cheaper than a custom coded website.
The company in need of a website purely as a blog to complement their existing website will be prepared to spend a little more on a theme and plugins to bring it’s look into line with the main site. The bigger the company, the more important it will be for consistency in the branding – think Coca Cola, Ford, etc. For this type of company, the budget available will be considerably more. For a local business, the budget will be considerably less bordering on free.
There are exceptions to all of the above, but as a general rule the above scenarios are true.