IMHO the Haynes manual is throwing away $20.00. Check out Rennlist.com or the Pelican Parts forums. There are a large number of DIY articles that are no cost and have better descriptions and pictures than the Haynes. I also noticed that Pelican sells the Bentley manuals. Based on my experience using one with my BMW, that would be better money spent.

You may also find the factory manuals in some of the Porsche for-sale forums.
When I had my 911, I purchased the factory manual on microfiche. If you could find a copy in microfiche, that would be a savings. I used the microfiche machine at the public library, and I am sure most library's still have microfiche machines.