Lower carb is the best way to help manage sugars.
Protein comes from animal products. The easiest sources are meats and eggs. Maybe nuts as well.
Cheap cuts of meat. Bulk buying of meats such as ground beef, pork, chicken. Eggs. Consider buying sale items (find out when your local store typically does markdowns). If you have a reasonably sized freezer, buy in bulk when items are on sale.
You may find a local farmers market can have reasonably priced produce.
Avoid processed foods as much as possible, as they are poor nutritional value.
Plan meals as much as possible to avoid wastage of foods.
Hope this helps.
I love this question. I also can have a fixed grocery budget which I means that I have to be careful how I spend. It's important to have a list when you go to the grocery store. Food companies spend a lot of money on marketing and place things just so at the grocery store so that we are tempted. I fall for it very easily myself and spend money I don't need to.
You can look at your weekly ads for the grocery store or two you are most likely to go to. They will have the on sale things. If it is something like lean protein (chicken, pork) then perhaps you can buy a bit extra when on sale and freeze it. Check out the 'short dated' section in your meat area of your store. You can find real deals there (ask the butcher too where it is) but it needs to be used within a day usually (or frozen). If you see a certain type of veg on sale that you like, you know to get it that week, etc.
My bill is always less when I stay away from prepared foods, chips, etc. That stuff adds up!
My grocery store has a website. On the website it has digital coupons. I load them to my card I use from that store (like Krogers card). It comes off at the register. Or you can cut couples from the paper. be careful not to buy things just because you have a coupon.
Some cost saving tips from me. :>)