Without a coach, I would say you need both. You just can't learn to vault out of a book ... if you don't have a "support system". We on PVP can be part of your support system, but it's just so hard to explain things with text.
I can read BTB2 and understand what they're talking about, because I already understand the concepts. But if you've never learned to vault properly ... yet ... then you need more than just a book. Actually what you need more than anything is a coach!
My recommendation to you is to find a part-time job on weekends, or sell your sports card collection, or do whatever you need to do to raise the cash. If you're serious about pole vaulting, you'll find a way. Rich uncles or understanding parents also help.
Just show them (by training hard) how serious you are about becoming a better pole vaulter.
There may be other innovative ways to get your hands on the book/DVD. Maybe talk to your school librarian about ordering it FOR THE SCHOOL?
I'm sure there's other ways ... ???
Kirk