Compared to WDW, which is our usual park, we thought the food at DLR was quite affordable and quite tasty. It is also MUCH better suited to snacking your way around, with the more compact park layouts, the ease of the mobile ordering at so many places, and a ton of really good QS selections.
A lot of the QS menu items we tried were large enough to share. The clam chowder in a bread bowl from Pacific Wharf in DCA and the jambalaya from French Market in DL ($15) were both easily enough for two and, with a side dish, plenty for three (myself, DD18 and DD11, so no tiny kids with tiny appetites). I really liked the food court type setup where Pacific Wharf is - we got the clam chowder from PW ($12) and an order of pot stickers from Lucky Fortune Cookery ($7) Bengal BBQ was pretty good too - we each ordered a skewer and split the hummus trio, and that made for a nice lunch for around $25. We also shared snacks at quite a few places - that raspberry Mickey macaron at Jolly Holiday Bakery actually tastes even better than it looks! - and generally spent under $10 on those stops.
Looking back on my notes, we spent $65 on food in the parks on our DCA day (for lunch, dinner and a snack - we had breakfast in our room) and $82 on our DLR day (lunch, dinner and bakery & Dole Whip treats). We might have been able to do a bit better outside the parks, but the in-park mark-up didn't feel anything like as bad as WDW (and the food was better!) so in the end we didn't bother leaving.
The biggest money-saver for us was sticking to free ice water, since we were there in August and are really not accustomed to the dehydrating power of "dry heat". Sodas would have added $10-15 to every meal!