IMO I would not add another baby to the mix. They cause more stress then they solve. I am a Mom of 4 and life is hectic. More then 2 kids adds alot of limiting factors into your life. Our world is designed for a family of 4. You'll have to get a bigger car (if you don't already have a minivan), eating out is more expensive, travelling is more expensive if possible at all (we used to be world travellers before having to by 6 tickets), activities that your kids can be in are limited (it's harder to afford swim lessons for all, or t-ball, that kind of thing), there is so much more running around, daycare costs, food costs, the list could go on forever. If your already finacially strapped another child would not help and would only put more strain on your marriage.
Your right there is no "perfect" time to have a child, but there are better times. If you decide that you really do want to have another child make sure that your prepared as much as you can be.
I don't mean to sound all negative. I love all my children, but life is so much more easy when Grandma takes 1 or 2 for a weekend :)