Like you, I'm in an area with little selection and nothing exotic. We get bonus points for the extra difficult challenge rating. ;)
I just took the Whole9 pdf seasonal guide to veggies and fruits from their "Paleo Poor" budget tips page and made my own notes on it. It already breaks down fruit and veg by seasonal availability and year-round, and it bolds the most nutrient dense "priority" items, and it marks the ones that tests have shown to be especially dirty (buy organic if at all possible) and surprisingly clean (no need to buy organic if you're on a budget).
I printed the list, and added dollar signs next to the "budget-friendliest" items: Broccoli, Brussels Sprouts, Cabbage, Carrots, Cauliflower, Collard Greens, Mustard Greens, Onions, Spinach... and Zucchini in the summer (can often get it free from gardeners).
This list is going in my reuseable grocery bag, so I won't have to remember all of this stuff when I'm wandering around the store. ;)
Because my selection here is so iffy, I also buy frozen Spinach (and it's so easy to cook with!). I sometimes buy Broccoli, Brussels Sprouts, Cauliflower, and Artichoke Hearts frozen if I find a great deal. And I cook with canned Tomatoes and Olives, which are pretty budget-friendly, especially when I stock up at Sam's Club.