I think you are doing the right thing...books are very expensive...well worth it...but pick one you really like and that suits your needs.
One moree thing, are you close to your teacher? If he/she supports you then ask them to request a complementary copy of the book..get the ISBN number for the text you want give it to your teacher.
9/10 they will send the teacher a copy since they hope the school will adopt the text...Additionally, have you asked your teacher what books they did reviesw and did NOT adopt...they usually toss them in a storage room...WASTED....
Just a suggestion...