FWIW, I married my husband when he had 2 kids with his ex, our first was unexpected, second even more so. I was sitting here thinking that if I had an only child, I could afford to take him to Jump for Joy. At $24 a visit, though - it just doesn't happen. Forget the zoo, and don't even get me started on college funds. Ours are 2, 5, 11, and 13. They better study hard and get good scholarships. Extra curricular activities are tight, too - both because of time and money. As an almost only (my siblings were 20 years older than me)I was able to do different activities every day of the week - my kids get to read and run in the sprinkler, although we splurged on a pool membership this year in place of mine and my dh's parent day gifts. I have to drive a gas guzzling van instead of an efficient little civic.
Also, what happens if your second baby is born with some special needs? (Mine was). Working suddenly wasn't the option that we thought it would be.
I understand where you're coming from - I was there. I'm with your husband now, though - I had my tubes tied to prevent any more surprises (we've gotten pregnant with condoms, the pill, and IUD just doesn't do well for me).
Another idea might be for you to go back to work to pay things off, then the two of you start trying again. It puts a bigger age gap between your kids - but it also means that the time and money constraints are spread out further apart.
S.