K.W.
Hi M.,
My son was 3 1/2 before we transitioned him. He never tried to climb out and was perfectly happy there. I read an article once saying most kids aren't ready until age 3. They aren't used to the freedom and don't know how to handle it. Also, I was having my second when he was 2 and not wanting to deal with any struggles at bedtime as I had heard many horror stories about bedtime battles due to transitioning to a bigger bed. I would wait as long as you can. Also, I bought a second hand crib at a hospice resale shop. It was 70 bucks with mattress!!! Try someplace like that or craig's list. Also, garage sales may be starting up soon!
Good luck with baby #2.