I wish you had done more research into fertility awareness based methods; with perfect use some of them have very high efficacy rates. The most effective, the sympto-thermal method, is 99.6% effective when abstinence is used during the fertile period and 99.4% when used with a barrier method during that time. And you don't need an expensive monitor (unless you want to use one), you can just get a basal body thermometer. The only other expense would be learning the method, with an instructor and/or through a book.
FABMs aren't for everyone but I think everyone should at least know (with accurate information) that they are an option =)