Professional Website Designers can charge a lot of money to put your business on the internet. Always consider your Website Design Budget, and Ask for previous websites that the designer has built, before handing over your cash.
The biggest reason to Hire a professional Website Designer is because they can do the same job that your job requires but much better. A business can do more for their business, without the need to pay thousands for a web designer that, can do only one job.
It's like if you are running a bakery, and need a professional pastry chef for an important ceremony to whip your wedding cake. You can go to the local baker and hire him for $500, but he may not be able to whip up anything worth having. So you'll need to hire a professional pastry chef to do the important role and save your cash in the process.
If you want to run your bakery as a successful business, you can hire the same professional pastry chef who made your pastries - but only if they have done the same job for you so far. A professional can also teach you things that you can't learn on your own, that will speed up your business (and save you money).

It's the same with web design. A business can hire a professional, but he should have done the same job or similar jobs for them and can do a lot more. A professional Website Designer can do a lot more for you in a day than the local guy can do in weeks.
The reason to get a Professional Web Designer is because, with a combination of design and programming skills, a website can do a lot more than a single person can do, so it's not all about how fast they can do your job - it's how much they can do for you. A Professional Web Designer knows all the tricks for creating your brand in the search engines, with all the search engine features and can build a site that is compatible with all, without breaking the site and with all the features and functionalities. A professional Designer will know how to design a site that looks clean and professional without looking cluttered and awkward. They can build a site that has all the features you need and the right tools so they are easy to use.
So if you're ready to hire a website designer to build a complete, state of the art website, it's worth it - even if it means starting from scratch. A good website designer will have his or her head above everyone else's in the web community and will have the knowledge you need to compete and win in the most competitive environment. And if you're ready to take the leap and build your website, then go get a professional!