While both procedures have the same end goal of surface hardening components, nitriding and carburizing employ different resources and methods to do so, with different results. Carburizing is a heat treat process that uses carbon, while Nitriding uses nitrogen. Generally, each process diffuses the chosen element into the surface of the component to produce a more wear resistant or harder surface. Nitriding is a better process for precision components, whereas carburizing may be a better choice for highly loaded coarse components [1]. 

Nitriding sometimes results in higher costs primarily because of cycle times and batch processing considerations. However, the cost increase typically corresponds to better properties. Another driver of cost is the cost of the base material. Nitrided steels tend to be produced from high alloy steels, which are usually more expensive [2].

In some cases, the carburizing process may prove more expensive, but the price of the base material (likely high alloy) must also be factored in [1][2].

[1]-https://blog.metlabheattreat.com/posts/nitriding-and-carburizing/#:~:text=The%20main%20difference%20is%20that,in%20carburizing%2C%20carbon%20is%20used.&text=Ion%20nitriding%2C%20on%20the%20other,is%20a%20more%20restrictive%20process.

[2]-https://www.eurotherm.com/en/heat-treatment-articles-en/what-is-the-cost-difference-between-carburizing-and-nitriding/#:~:text=For%20Carburized%20steels%20you%20would,processing%20and%20long%20cycle%20times.