I hate 3 ring binders for shop manuals. Binders are just crummy, all that work you've done to have it in an ugly Trapper Keeper?
What about spiral bound? I have all my manuals printed up at Kinkos and spiral bound, that's my fav way to have them. You could sell the book shrinkwrapped as loose leaf paper and allow people to have them bound however they like. Most any print shop has a wide range of binding options, including book format, spiral and 3 ring.