I can't afford to stay at home myself, but on your budget you can use any advice you can get.
A few things we do to save money:
Have a garage/yard sale periodically to get some cash - w/ kids you always have toys, clothes they outgrow that you can sell.
Coupons - live off whatever happens to have the coupons out that week, or on sale. I almost never buy anything that is full price. I watch the clearance racks like a hawk (Target is great for these) :)
For a night out treat, we go to places that have kids eat free - there are some websites listed in the business review section of mamasource, I think, or google "Kids eat free." On other nights, my kids are picky, skimpy eaters anyway so we buy one kids meal and they split it - it is wasteful to buy them each a meal anyway b/c they never eat it all, my kids eat about half anyway so why waste money and food? Bring home your own leftovers which usually are enough for another meal so it makes it more cost effective to allow yourself out every once in a while. Also, my kids rarely eat much of their side items so I feel free to just order my main course and eat their veggies. Hey, I paid for it, can't let it go to waste!
Use the library for entertainment, or the $1 redbox video rentals when you need to spend money for a movie. If you have a neighborhood pool, kids can go there practically every day for free recreation.
Hope this helps. Oh, and my kids LIVE off peanut butter practically (on crackers, bread, toast, etc.) and it is nutrition on the cheap. Rice, beans, noodles, mac and cheese, anyone? :)