If you don't care to save the drawing (.drw) file for each instance, just replace the model in the drawing you have, export the DXF, replace with the next model and repeat.
If you do use this technique, you will need to rename the DXF as you export it to match the current instance (the tricky part).
In theory, you could create a trail file of the first few, expand it to include the rest of the instances and run the trail file. Getting this to work properly could take more time than running 50 DXF's, but if you ever have to do it again...
