For most small time Internet marketers hiring a SEO consultant seems unnecessary and most could not even afford one anyways. But here is one way to view hiring an SEO consultant as a long term investment.
The idea is to hire a consultant to help with your initial website and then learn all the steps that they do to help get your site ranking very high. Then you can repeat the steps yourself on all your subsequent websites.
Obviously this works only if the person shares all of their SEO tips and techniques with you. You could put this clause in your contract that you sign with them that they will fully disclose all the steps that they take and the websites that they use to help get your website ranking well.
If you view hiring a consultant this way, then most small time Internet marketers cannot help but view hiring someone like this as a great long-term investment.
Since most Internet marketers have dozens of sites, this can be a great way to shorten your learning curve by learning from someone who is already mastered this field. Learning from a master can shorten your learning curve dramatically.
Hiring an SEO consultant is cheaper than you think, and in some cases you pick and choose certain packages. And if you learn enough about SEO, then you could open up your own consulting firm as a great way to supplement your income. In fact many SEO experts make a great living doing just this.