I think it depends on what you mean by "standard". I've worked with a few agencies that have developed small sites for around £2k. For that you get a dedicated account manager, a designer and coder and the site built within a week, following a process of design, review, amend, review etc. Here in London a top end PHP developer can be on £250-£400 per day, .net developer on more, designer on £300 etc so £2k is arguably fairly reasonable. Some agencies also lease their developers for around £1k per day.
If you were a one person operation building a WP site you could probably build the same site in a day.
The difference is that the agency usually has a pool of people with specific skill sets and experts are expensive.