Do you have a newer version of MasterCAM or a similar NC software platform? You can sometimes create 3D solids in AutoCAD (I'm faster on that platform for some reason), save in normal .DWG format, import into MasterCAM, then re-save as an IGES file. I've had this work completely sometimes, and other times I've had to fill in some gaps in the IGES geometry. If you do follow this, make sure you flesh out the wireframe and check the part for continuity. Usually the errors in the translation were blatant.
Otherwise, just pay the cash and buy the converter. It's likely the easiest and most efficient method.