If you want to learn about your cycle and fertility signs and whatnot, start by reading Taking Charge of Your Fertility. Dollar store pregnancy tests are just as good as $15 tests. Digital tests are less sensitive than regular ones. First Response Early Response are the most sensitive. http://peeonastick.com
has lots of information about the different pregnancy test brands, and also about OPK's. But I wouldn't worry about the OPK's. If you really want to know when you're going to ovulate, learn about your fertility signs and save the money on the kits.
Really, what everyone else said is pretty valid. But since you said you wanted to know everything, I thought I'd let you know where to start.