The first thing a lot of people love when they first see Wordpress is the word "Free" - And it's true you can get Wordpress for free. However it's not all roses. Wordpress comes with a host of issues which are really worth taking into consideration.
Wordpress has a huge issue with Security! Wordpress is the most attacked platform on the Internet and although there are regular patches and updates, it's record is not great. In fact Website Security company Sucuri reports in 2017 83% of Wordpress sites were infected, up 9% from the previous year.
While many of these infections are probably down to ignored updates and patches, if web security is important to you, you're probably better off choosing a more secure platform. Paying your developer for keeping your Wordpress security up to date soon begins to outway the money you've saved by choosing a free Content Management System.
Security is not Wordpress' only issue though - Wordpress relies on Plugins! Wordpess at it's core has only very basic features and while this is fine for a small blog for anything bigger you will need Plugins! And probably a lot of them.
There are over 50,000 Plugins to choose from, many of which cost money (eating away at your savings for not paying for a content management system) and many are not updated regularly. Having plugins that are not updated regularly can cause all sorts of headaches and if the plugin plays a big part in your site can take it offline all together until the plugins author has the time to fix the issue.
With security issues and out of date Plugins come more issues. You're not only prime target for hackers but you're a prime target for Spam. Without premium plugins Spam continues to slip through and sometimes embarrassingly onto your website comments sections.
So yes, Wordpress is free but maintaining it is very far from it. What you save in the beginning, Wordpress will take from you in Theme and Plugin management, Security issues and Spam.
In the long run, Wordpress often becomes the more expensive option.