Both ways can work. But unless you want to do web design as a hobby or as a side gig, a DIY website will take up a lot of your time. And the results, at least to begin with, might be less than professional in appearance.
How can you keep the cost down?
Start with a good quality off-the-peg WordPress theme. Some themes are designed to be used as is, some have a lot of built in customisation options. Make sure the theme you choose, is well coded and focuses on highlighting your marketing message. Bells, whistles and the latest design fad are unlikely to help you win clients.
Photos and images
If at all possible, take your own photos. For instance, on your about us page put photos of yourself and your team. On your services page you could put photos of yourself working with a client. Or if you’re a designer you could display some of your best designs. On your contact us page you could include photos of your premises or sign written vehicle.
If you need some generic photos to brighten up your blog you could try Unsplash.