I agree with you shouldn't buy shares in a plane at this early stage until you figure out what type of flying you will be doing, you might end up loving aerobatics and not flying cross-country so much, therefore a different A/C required.
In saying that, I have known many student pilots who have bought share's in aircraft that are used as line aircraft at aero-clubs and flying schools, the advantage of this is you get a very cheap hourly rate, students and instructors using the aircraft pay for the planes maintainance cost's and insurance etc etc, I'm not saying this work's for everyone but I do know people who have done it quite successfully, for example I know someone who bought a CT4 Airtrainer share for $2700, did 100hrs CPL training for $85hr + instructor costs and it was aerobatic aswell, that was a few years ago now and a very good deal at the time but it gives you an idea of what is possible.
Just something to think about