Just wanted to make the point, in case someone hadn't considered it, that I have found many comic books in my public library and the extended system it is part of. Because comics aren't considered literature, or even "serious reading" by many people, the library might not be such an obvious source. In my library, the teen/young adult section has the mainstream DC, Marvel lines. But in the stacks, I have found many of my favorites.
So if your hesitant about throwing down $15 on a trade (or even $3-4 on a specific issue) without knowing anything about the comic or the genre - or you want to catch up in a long running series w/o shelling out a ton of cash - explore your library.