Re: Mercury Manual
I may be able to offer a little bit of insight, as I went through the same thing with a 1980 Johnson. First I bought one of those generic one-size-fits-all manuals that sell for around $25 or $30. I was really displeased with that as there was a lot of information missing.
There are online stores that sell original factory manual reprints for about $65 to $70. One of those would be just fine, but I'm cheap and that seemed like a bit much.
Then someone here on iboats pointed me to an ebay store that happened to have the exact original factory manual I was looking for, and for only $30. That's the way to go if you can find your model year.
There are also a plethora of people on ebay selling manuals on CD for $10 or $15. I have no experience with those, but judging from the descriptions it sounds like they've just scanned the generic one-size-fits-all manuals. I may have to break down and give one of those a try though, as I'm currently looking for a manual for a 1973 Merc 7.5 HP.