Hi opsmgr - and welcome. Feel free to raise that head above the parapet.
Why is the course only 25 pounds? Put simply, I compared it with the price of a good book on proofreading rather than a course as such, as I think this course has more in common with a tutorial. Of course, a book isn't updateable and accessible anywhere in the world (I mean ... if you forget to take it with you ...), and doesn't link seamlessly into a community of like-minded folk.
The proofreading course I did way back in 1995 cost me a few hundred pounds (and that was a lot of money then), but when I opened it up I found that it was an English course telling me stuff I already knew, but with a few proofreading symbols nailed on at the end.
So when I actually started proofreading I didn't know how unprepared I was. The course didn't tell me how great a part typesetting and style play in the proofreading process. I decided to write my own that covers not only typographical aspects but also the parts of English that trip people up.
Also, some of the larger courses advertise in the national press and have many employees, which someone has to pay for. They also have mentors, which is great, but this forum is my mentor.
So in a nutshell, I think the price reasonably reflects the nature of the course. I never wrote it to become a millionaire but in case you're interested I need to sell just one more to reach that milestone