Nah, commercial airliners don't fly pretty much everywhere they fly between airports on predetermined routes. Through air traffic control "sectors" One of the things that is hard to understand for all of us who live so close to the civilized world, is how much of the world is uninhabited and poorly understood.
As many have pointed out, Google has used clickstream data from their toolbar for a number of years.
Also, Google has used the links provided by hub and search pages to find relevant sites within a niche. They have happily indexed links they discovered on those pages, and then removed or penalized the pages that pointed them to it. It's OK, of course, because any SERP not provided by Yahoo Google or Microsoft is termed "spam"
I would say value for the money is not the primary challenge. Expertise is expertise.
You are buying a specialized marketing campaign, hopefully devoted to raising your targeted organic traffic from search engines.
You should expect to pay the consultant's hourly rate. You might receive recommendations for other services like content creation or link building, either performed by the consultant, or sourced on your own.
You don't have to pay a monthly retainer. I would preferably make an RFP to several seo firms for a proposal that outlines their approach to your site. Generally, you are looking at an engagement of longer than 1 month. Like any marketing campaign, testing and measuring is crucial to best results.
http://www.woorank.com will show you how you stack up, and give you some hints, but if you "need" SEO and you have other duties, and you have budget, hire this out. You likely will not outrank me if you are brand new to the techniques.
Auomated services will give you some tips, that will undoubtedly improve your rankings. Submitting forms will not give you an understanding of how to align business goals with search engine algorithms. Nor will it show you how to determine a worthwhile link from a crap one. SEO is a real discipline, a sophisticated art, and a process for repeating results that has been improved over dozens of iterations by the consultant.
SEO and SEM are not unrelated but they success in 1 has little to no causation of success in the other one. SEO and SEM are often connected by the same consultant. I do both.
You should bid SEM and SEO out separately, if somebody bids on both, you could seek a discount. EXPERTISE IN ONE DOES NOT MEAN EXPERTISE IN THE OTHER.
Wizards explain what they are going to do and why, just not how.
In my experience, the better SEO's treat the process more like a developer would bid for a contract programming project i.e. Scope, specs, change orders, deiverables, etc. If you feel like the potential hire is kind of talking like his magic is just going to rub off on your site.
It is perfectly legit to pay another consultant to evaluate your proposal.