Wanting to make my client's job as simple and cost-efficient as possible, I then looked into Wordpress plugins, but there was nothing that seemed to match his requirements.
And then I found it! A Worpdress LMS plugin from LearnDash due for release in January 2013 which looked an exact fit.
OK, I haven't tried it yet, but given that this is a company with extensive learning industry experience that has consulted for Fortune 500 companies and has invested time, money and effort into developing this LMS, I'm guessing it will do what it says on the tin and more.
The WP LMS feature list is impressive. I'm really looking forward to testing the LearnDash LMS and reporting back to my client. I think he'll be pleased that he can create unlimited courses with an integrated payment system, easily manage and communicate with users and do all of this without paying large monthly fees.
Personally, I'm looking forward to having the technical support of a company that not only builds the system, but also has experience of the learning industry to call upon.