The cold gas dynamic spraying process provides an advantageous solution to the deposition, and additive manufacturing, of metals. Namely, it provides a reduced reactive environment, simple operation, and high deposition rates. It is known that the deposition efficiency of the cold spray process can be substantially increased using helium instead of nitrogen as the process gas. However, the use of pure helium can be cost prohibitive and commercially available helium recovery systems constitute a major capital investment and cannot be used with portable systems. This work focuses on the development and use of a novel, in-line gas mixing system, designed to provide a blend of nitrogen and helium at any ratio. Deposits produced with different gas ratios are investigated through particle velocity measurements, deposition efficiency, coating porosity, and coating hardness. The experimental results show that helium, even in lower percentages, can have a significant effect on deposition efficiency and coating quality. From the results, a cost model is presented which, when provided experimental values and user costs, can be used to identify the nitrogen–helium ratio that will produce the lowest overall coating cost.