Hi kulagabe,
It is probably best to not export the mesh nor point cloud, but contour lines as DXF instead. These are most commonly used by engineers and surveyors (and plotted on maps and plans).
Here is what you need to do:
1. Process you imagery in PhotoScan and compute a DEM
2. Generate contours for the DEM. Open the DEM in Photoscan by double-clicking on it in the workspace pane, then click TOOLS > GENERATE CONTOURS. Choose your desired interval (e.g., 1 will give you a contour line for every meter).
3. The contour lines are stored as a group called Contours within the SHAPES folder. Right click on the Contours group and click EXPORT LAYERS. Choose DXF as file format.
DONE.
All the best.
Regards,
SAV