I know you said you can't afford regular lessons, but can you swing a couple? I think it's really important to at least be sure you have yourself "set-up" properly. Have someone check your hand positions, show you a little technique, stuff like that.
After that, go ahead and get the Hal Leonard book that was edited by Ed Friedland:
http://www.amazon.com/Leonard-Bass-M...9082145&sr=8-1
Can't go wrong with this book. It's what I use with my beginning students.