When selecting keywords to optimize for natural (organic) SEO, the results will be much better if an overall strategy is applied rather than just focusing on each keyword as an isolated entity. This is a fairly recent phenomenon. It’s related to the sophisticated new “meaning-aware” indexing algorithms some of the search engines (notably Google) are starting to use now such as “latent semantic indexing”.
When Google arrives to index your site, it already knows the entire vocabulary of your industry! It even knows that vocabulary in context of the relative importance of various individual key phrases or keywords.
Therefore you should actually make a point of optimizing the most “important” keywords that relate to your industry even though they are ridiculously “expensive”. You optimize them not because you expect to receive high rankings or traffic from them any time soon, but because they make it clear to Google that yours is an “authority” site. To make the most of your digital marketing investments it would be best to hire a SEO agency. They know all the ins and outs and will surely not make the mistakes you would.
When you do this you are establishing a clear context that will synergize all of your related keywords by showing exactly how and why all of your pages are relevant to a variety of search keywords.