You probably already do this, but use store brands for everything! True, there are a few things I've found that I like the name brands for more, but nothing -not one thing -has been a total disaster! Diapers particularly are HALF PRICE compared to national brands and so is formula if you're using any of that. I've started at least trying the store brand for everything -I used to always use Tampax Super and have found that CVS, Kroger and Target brand tampons are exactly the same. Canned veggies and frozen veggies and fruits are the same, body washes, etc. I've found I actually prefer the thinner store brand toilet paper to the ultra thick Charmin -and I use store brand paper towels too.
Make sure you have a "store card" for any grocery stores you visit or drug stores. You will usually get coupons from them to use at those stores. Check out any large area farmer's markets too -often they have much better buys on produce and meats. Costco will cost you $50 initially for a membership, but for a family of four it may be worth it. They happen to carry a lot of stuff we eat a lot of, so it's a deal for us -especially for canned drinks, tp, paper towels, trash bags, cleaning products, detergent and meat. They have AMAZING deals on nice beef and pork.
If you're in Minnesota, perhaps you can cut out AC for the summer and open the windows and use some fans.
I don't know what your education or work experience is, but be objective -if you have experience or a degree in something that there you see jobs for out there -go for it. Dad can be a stay-at-home dad for a little while -at least until the market picks up!