The material costs (the $300 per kg of titanium suggested in another comment) are only a small part of the overall expense. Electron beam sintering printer time typically costs $100-$200 per hour, and a large build can easily take multiple days.
After the printing itself, one will have to remove to loose powder, which for small cooling channels in the walls of the combustion chamber is very challenging and time consuming.
After that, some post-processing may also be necessary. One process for achieving the greatest strength is hot isostatic pressing, when the part is baked in a furnace in a retort filled with a very high pressure inert gas.
Specifically for rocket engines, it is also desirable to have a layer with the high heat conductivity on the inside, typically made of a copper-based alloy, and the external structure from a higher strength material. This means either bi-metallic printing, which is a rather niche process, or some metal deposition process over the printed part.
In addition to this, there is usually quality control, for example, high resolution industrial computed tomography, to make sure that the invisible internal features have been fabricated and cleaned out correctly.
In addition to the additive steps, it will also be necessary to machine the features which are impractical or impossible to build sufficiently accurately.
After the printing itself, one will have to remove to loose powder, which for small cooling channels in the walls of the combustion chamber is very challenging and time consuming.
After that, some post-processing may also be necessary. One process for achieving the greatest strength is hot isostatic pressing, when the part is baked in a furnace in a retort filled with a very high pressure inert gas.
Specifically for rocket engines, it is also desirable to have a layer with the high heat conductivity on the inside, typically made of a copper-based alloy, and the external structure from a higher strength material. This means either bi-metallic printing, which is a rather niche process, or some metal deposition process over the printed part.
In addition to this, there is usually quality control, for example, high resolution industrial computed tomography, to make sure that the invisible internal features have been fabricated and cleaned out correctly.
In addition to the additive steps, it will also be necessary to machine the features which are impractical or impossible to build sufficiently accurately.
Together, these steps add to a significant cost.
Some of the above processes can be seen in this video: https://www.youtube.com/watch?v=7pXEf0wHU1Y