The reason I have so many manuals is the pictures and drawings. The factory, and say Chiltons, manuals use a lot of photographs, wheras Haynes manuals use a lot of line drawings. Sometimes the clarity of the photo is important, and other times the simplicity of the diagram gets you right to what you need.
Another consideration is the photo's themselves. If I take a photo of the carbureter and so does Bob, we are undoubtedly going to be at slightly different angles and focuses. The difference between the photos may just emphasize the point you need.
With this in mind, and the availability of manuals on e-bay, I would recommend limiting yourself to $3-5 each and buying 2 or 3 different manuals, with at least one of them being the factory service manual for the appropriate year. In the days before e-bay I paid $400 once for a Kadett purely for the factory manual and AC system that came with it. These days, there is really no need to spend much more than $5 for an aftermarket and maybe $15 for the factory manuals
Another option that worked for me when I was broke in college was the library. I actually still have photocopies of 3 or 4 whole books that the college library got in for me on the book exchange program. A 200 page book that has been out of print for 20 years only costs $10 to photocopy cover to cover, and you may never be able to even get your hands on the book again. Add a three ring binder and you now have more valuable information, something you can't have too much of.
Another HUGE advantage to photocopies, one I use even when I have the manual, is that if you photocopy the procedure you are using you can get it greasy. You can also take notes on it, you can check-off steps as you get to them, and you only have to hold on to a page or 2 at a time, easily fitting under the windshield wiper for a convienent sheet holder. I take photocopies along any time I am working on someone else's car because they can take their own notes as we go along and 9 times out of 10, if their notes are good, I don't have to stick around for the reassembly. Compare 30 cents for copies to 3 hours of shop time, and you can afford to buy a copier in short order.