I recommend buying things like beans, canned veggies, pasta, rice, cereal, spices, etc. in chain stores, especially when they offer double coupons, as above.
Costco in Brooklyn, Hackensack (Serves Teaneck) and Five Towns each have a kosher bakery, and offer kosher meat and cheeses at good prices.
The only things I typically need to buy from a kosher store are cheese and meat and deli. I do my own baking and cooking on most things, and save a lot like this.
Pic n Pay has cheese at very low prices, and I don’t know if you eat from the hashgacha of Rabbi Gavrielov (a Chabad hasid), but they’re meat is also cheap. They sell Marvid and Empire, as well as Jacks Gourmet, Tirat Zvi, etc.