The Wordpress CMS is free to use. The costs for a Wordpress website consist of:
You got basically 3 options. You can buy a standard theme, you can make your own theme or let someone else create your Wordpress theme. The most standaard themes are priced between $29 - $59 and must be payed yearly.
Building a normal custom theme yourself takes between 20 - 80 hours. If you hire a company to design and build your theme it will cost you between $2000 - 8000.
To keep your Wordpress website up to date and secure it is important to maintain your website on a monthly base. It toke 1 or 2 hours a month for a Wordpress installation.
The hosting of Wordpress website will cost between $75 - $200 on yearly base.