C.G.
Please don't try to convince him. When it comes to having a baby, you need 2 to say yes, but only 1 to say no. I think you should talk to him more about it, finding out if he really wants a second or if the economy is an excuse.
I think if you talk him into it before he's ready then he will resent you, possibly resent the baby, and would definitely not be the help you need with 2 children.