Building your website
This may sound a little obvious, but if you have never created a website before, consider whether the combined costs of: (a) buying software, (b) learning how to use it and (c) spending time building your site are higher than the cost of having it professionally created by a design agency.
If you decide to go it alone there is a plethora of choices of software. Most people will have heard of Adobe's Dreamweaver, but may not be aware that that programme on its own might not be enough to produce the site they have in mind. There are free alternatives (in fact you can design a website using any text editor, although this is an extremely laborious process and requires a lot of knowledge). Examples include
but these also require a certain level of knowledge and are not really aimed at beginners.
There are various options for the website-builder who does not want to understand how the web works, and just wants a generic website. A web search for "build your own website" will bring up plenty of ideas - too many to list here. You will still need to learn how to use the software, and it will limit you to particular designs but it will get you online.
There are free online community-building software packages which will make it possible to get a blog up-and-running in a few clicks. But if you want an truely individual site you will need to invest a bit of time and effort to achieve the result you are looking for.
In summary: there are free options out there on the web, but they may not be the best option for you. Consider all the cost factors of setting up and running your own site. Do you have someone who can do it for you or will you be stopping your usual business to work on your website? Do you have someone you can call on if it all goes wrong or you get stuck?
It is worth considering that not everything that is free is truely free, and websites created with free software by inexperienced designers may not be the best way to present your business to the world.