if he is 2 yrs old now then he can probably use a step-stool. but introduce it to him early enough that you can help him for about a month just so he gets the hang of it. if you are going to use the same crib for your new baby, then i would just suggest getting a Toddler Bed instead of the interchangable cribs, because then there's no need for the crib part of it. unless you get one that changes from a Toddler Bed to a Twin sized bed, then it may still be useful. if not i would just recomment using a toddler bed. they are a lot cheaper to buy and its really all you need for right now. like i said, if you arent going to use the crib part then its pretty much just spending extra money.
if you are okay with Hand-me-downs, there is a site www.craigslist.org you can look up cribs/ toddler beds or anything else you need on craigslist. people just sell stuff they dont need. i saw 3 Toddler Beds on there a few weeks ago. it was $30 for the frame and $40 if you want to include the mattress. or you could take all 3 with mattresses for like $90. thats just an example i saw. but i wish you luck. congratulations though. hope you work it out. :)