You buy veggies for your guineas! How about you treat yourself to some too?
Are there any freebie neighbourhood food shelves around you? Or actual neighbours with too much fruit on their trees/bushes? Or Food Savers, or similar local group, running on FB from whom you can get food that was otherwise going to be thrown out? Here those groups procure from stores, not from dumpsters. The Food Bank has first choice, then Food Savers. Here there are also websites where people give things away (maybe Craigslist in the US?), and sometimes people give food away, either because they have too much garden produce, or they're moving, or their granny passed away and they're clearing her kitchen and pantry. Some of them even give food plants away - for your yard! I know that would be more difficult where you live because of the harsh winters, but there will be winter-hardy types. Apart from Food Savers since I'm not on FB, these are all methods I use to save money on food-shopping.
There are also wild herbs, commonly known as weeds, and you have a yard. Of course they're not all edible, but of those that are, they are jam-packed with vitamins and trace minerals! Far more than in store-bought herbs and lettuces.
Maybe one of these ideas can help a bit? If not or these ideas are not up your alley, just ignore!