For a limited run you could have soft tooling done. Use the model to create a rubber mold (-) which is used to create another mold (+) that used to create the final soft tooling for the limited run. May be good for a couple of hundred castings. Key here is taking shrink into account for all the materials used. This has to be done in the 3D model for the printing so it will be "transferred" to the final mold and base. Keep in mind that draft should be taken into account too. Straight walls cause the part to "stick" to the mold and not come out. The other option is using a Lost Wax process where wax is used to creat the mold. It is destroyed for each part but the material can be recovered for new molds. In addition, sprues need to be designed in for the material flow along with vents to ensure the matieral flows into all the cavities. And we thought castings were straightforward!