This point is not about the suitability of a 3D printer for a silencer. However, I teach a 3d printing class and I want to point out that 3D printing is not that expensive.
One of the most popular hobby-grade printers is the CR-10 series. Depending on the model, it will cost between 300-500 dollars. As far as the software, one of the popular software tools is Tinker-Cad, it is free.
Yes, the purpose of Tinkercad is to push the user to the Auto-Cad tools (it is owned by the same company. However, for something like a silencer, Tinkercad would be entirely adequate.
Yes, there are more expensive 3D printers, While I have a CR-10, the school I teach at has a much more expensive one. Frankly the schools unit cost about six times as much; however, I don't see it as being six times better (If you are wondering, we got a grant and they chose the printer).
3d printing does not have to be an expensive hobby.
All that said, I don't think 3D printing is a good way to make a silencer. The issue is that It will not be as durable as a "metal" silencer and, with the tax issues and laws that regulate silencers, it makes sense to make them out of more durable material.