You might find this post from Elegant Themes really helpful

As they say:

Despite being advertised as a free platform, WordPress pricing isn’t quite that simple. Sure, you can set up a free account on WordPress.com, however, the site comes with limitations that many users will likely outgrow. Then there’s the famous, free, open source, self-hosted WordPress.org software. True, it’s free to download, but (at the very least) you must purchase a domain and hosting plan if you want your website to be available to others. Over time you will almost certainly want to purchase a premium theme, plugins, and potentially custom development or support. All of this is to say that when considering WordPress website pricing, you can’t just look at the marketing materials. That’s why in this article, we will break down the real expenses you can expect to accompany a self-hosted WordPress website.

They go on to say…

Some agencies and freelancers may not work on flat rate, but hourly, and that same site might cost $50 to $150+ per hour. In talking with and researching WP pros who work on contract, we’ve found that a good middle ground for hourly pricing is around $75. However, if you are dealing with an agency or design/development firm, prices will likely be close to $200 to $400 per hour because the money is filtered and split across the organization to pay those involved.

I charge $75 per hour and my standard proposal is that it takes between 10 and 20 hours to build a simple site, depending upon features required.

Bottom Line:

Taking all of these factors into consideration (and being unable to truly price the value of you and your team’s time), we think that the overall cost of an active and successful WordPress website can be as low as $800 if you’re conservative and up to $24,330 if you go high-end all the way.