Costco is also our go to for staples, I can get all my grains, nuts, seeds, legumes, beans, tomato sauces, and frozen fruits/veggies their in bulk all organic! One trip usually lasts me all month for those items.I would not recommend them for fresh produce though.
For fresh produce I'd love to use the farmers market or my garden like I did all summe. For the winter months if you can find a FM or CSA that'd be gold. For now we walk to stop and shop and raid their natures promise section for vegan staples like tofu, tempeh, and tofutti items, as well as fresh organic fruits and veggies. We try to make as much as we can from scratch using bulk items. All in all we feed a family of 3 off of about $500/month doing this.
Vegan cookbooks are my new addiction and have helped us keep things interesting and nutrient rich w/o breaking the bank. Check out 'The Lusty Vegan'
Good luck love!