From a purely economic point-of-view, renting is cheaper than owning. So don't feel like you're wasting money renting a plane during your lessons. In addition to learning to fly, you'll also be learning about airplanes. This will make you a more discriminating buyer - you'll know better what you like and don't like about an airplane's condition, equipment, handling, performance, etc.
I didn't buy an airplane until after I got my license. Looking back, trying to learn to fly and learn to own would've been a daunting task. Not to say it can't be done - some people buy a plane and learn to fly in it successfully. Others get their PPL in 40 hours. I'm not one of those people.
Renting (for me) was not a problem when learning to fly. Lessons were scheduled weeks in advance. I knew what I wanted to do and when to do it.
After getting my license, renting no longer worked for me. I didn't know weeks in advance that it would be a nice day to fly my girlfriend to Nantucket for lunch. So owning afforded me the flexibility and freedom I desired from being a pilot. The expense was greater, but worth it to me.
But back to you - the both of you should concentrate on getting your licenses first. There's a lot to learn and agonizing over which plane to buy, or how expensive the repair will be to the one you bought will be distracting.
After you get your license, you may find that a 150 is not the plane for you, that a 172 or something bigger is really what you had in mind.
Or, you may find that the 150 you've been renting all along is exactly what you need, and why did I wait so long? <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />
Who knows? While getting your license the right airplane may come to your airport for a visit with a "For Sale" sign in the window. Sometimes you find the best things when you stop looking.
