Yes, On Page SEO is extremely easy if you follow those specific guidelines.
And yes, it is the foundation to any successful SEO campaign (after keyword research, of course).
Usually I'll charge a one month's fee to my clients for the research and On Page Optimization. But some clients come to me for just the On Page Work. It tends to work out to $100/page.
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But if you have a client who's site is a high PR, has decent domain age, and already has fairly developed content; they can truly benefit from just the On Page Work. Of course I'll upsell, but this is a great way to show your SEO value/worth/knowledge, which can lead to them bringing you more sites or referrals.
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On IM and SEO forums, you might not have the best of luck. There is a ton of content posted all over these forums, and that's how most SEO books start out.
However, there's always a price someone is willing to pay, who would rather have the work done than do it themselves. Could be worth trying out.