Honestly, in my experience and as always your mileage may vary, the key to keeping the grocery bill down is simply this.
Stop obsessing over the word "Organic". By and large, if you are embarking on a Whole 30, your eating habits previously were fairly awful. You have already been been exposing yourself to the worst foods/chemicals you could. Frozen vegetables are fine. Beef that isn't labeled "Grass Fed", or "Pastured" also won't cause your heart to spontaneously stop.
Embrace that simple concept, and the Whole 30 is actually *significantly* less expensive than the current diets of those for whom it does the most good.
Is grass fed, pastured, "certified" meat and produce healthier than the standard found at your local supermarket? Sure. I won't argue that point. Is it something you should stress over with your Whole 30? No. The Whole 30 is a large enough change in ones habits that adding an additional stress is unnecessary. I had a friend whom I introduced to the Whole 30 actually give up half way through because she couldn't find the meat and produce locally, and was having to drive an hour and a half to do her grocery shopping. I tried to explain/convince her that it wasn't necessary, and she kept referring me back to these boards, and how she *needed* these things to make the whole 30 work. We are talking about a single mom, who works two jobs. Adding 3 hours of drive time to her week... it was just too much. Maybe she wasn't committed enough. Maybe if she saw more people advocating plain old supermarket beef/chicken/eggs and frozen vegetables, she would have just stopped by Wal-Mart where she normally shops, and she could have completed the Whole 30, and made those healthy changes.
I love the Whole 30, it changed my life (Sadly it wasn't permanent, I fell back into old habits and am starting another whole 30 sept 1st), and these boards are an absolute wealth of information, and the people here are just wonderfully supportive. That being said, I think sometimes we focus a little too narrowly on the minutiae, and forget about the overall benefits and goals the Whole 30 is helping us to achieve.