Depends on what they are using and what you want to give them
1) You can export the cross sections - if you select the sections in the sheet view graphically from the sheet view - it will export to DXF / DWG Model Space.
2) You can export the cross sections - if you select the Sheets in Project Explorer then the sections will be exported to DXF / DWG in Paper Space
3) You can export the Radial Surface as a DXF or DWG 3D Faces model to AutoCAD. You cannot export it to LandXML or TTM or any other surface format because they dont support radial surfaces - so the 3D Faces is the best bet.
4) You can send your client a VCE file and they can use the TBC Free Viewer to view and manipulate the data - and hopefully see the value in TBC and purchase a copy :-) !!!
Hope that this answers the question
Alan