If you want to create a website without SEO penalties that serve up quality content that people are glad they land on. If you use a WordPress template many negative SEO implications go with that, a few reasons are using a template can score duplicate content penalties because of the code as that template may also have been used by someone else to create SEO spammy sites and has been blackballed by the search engines.

One way to cut down development costs is to use a certain kind of template, not a WordPress template that is in use by thousands of users. The template you can use is just a standard HTML/CSS bootstrap template, you can mix and match multiple objects from numerous bootstrap themes. These typically won’t be adapted in dynamic cms platforms so they won’t have a lot of spammy mass content users out there, they won’t have over-saturation and when they are used they are typically modified so heavily they no longer score any duplicate code content penalties. These are just HTML themes that you can program into WordPress as a WordPress template

You can mix and match different elements from different bootstrap themes. This will avoid any possible duplicate content issues, template oversaturation, spammy SEO issues from others using a WordPress template etc.

There still is custom programming as you have to build these out into WordPress templates. When you use a bootstrap theme they are still very much custom as you use a lot of different objects and you customize it etc. It is like starting from a quality HTML base but in the end, you get something fairly unique that looks very good at a fraction of the cost and it avoids all the SEO issues that come from using an oversaturated WordPress template. If you were to use a WordPress template then somebody also decided to use that same template to commit what the search engines deem as suspend-able behaviour it could destroy your website rankings or even result in a ban to as they could consider your site part of the same operation and then using that template to link back to other domains could also negatively impact the sites it was linking to.