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The edible grasshopper, Ruspolia differens (Orthoptera: Tettigoniidae) is food and a source of income for many people in East Africa. Recent laboratory experiments have succeeded in rearing them on germinated finger millet (GFM). However, long-term mass production on such a feed would be costly. Incorporating inexpensive and locally abundant agricultural byproducts into GFM could be another option to lower the production cost while maximising its profits. We experimentally evaluated the effect of blending GFM with 25%, 50%, or 75% by weights of three agricultural byproducts (soybean hull meal, local brew waste and dry maize cob) on the survival, developmental period, adult wet weight and reproductive performance of R. differens. A total of 390 R. differens were reared individually on each of the dietary treatments, including GFM as control, till death. Data was analysed using generalised linear models. Overall, the R. differens performed optimally on GFM supplemented with dry maize cob, and poorly on GFM supplemented with soybean hull meal. However, performance varied across supplementation levels with dry maize cob. GFM supplemented with 25% dry maize cob yielded the highest overall survival (86.2%) and highest 14-day-old male adult wet weight (0.54 g). While the shortest overall developmental period (86.8 days), highest fledgling adult wet weight (0.53 g), and highest 14-day-old female adult wet weight (0.82 g) were observed on GFM supplemented with 50% dry maize cob. Supplementing GFM with 75% dry maize cob resulted in the shortest pre-oviposition period (10.6 days) and the highest percentage hatchability (82.7%). Generally, supplementing GFM with dry maize cob greatly improves the performance of R. differens. Our findings recommend including dry maize cob on the list of low-cost substrates for the farming of this endangered valuable edible insect species.