meshlab is awesome but a bit intimidating. It is not designed for ease of use exactly.
from meshlab you can export a DXF for autocad. You will get a 3d face for each face of your model.
if you want a solid model, that is a whole different issue.
You will need something that can convert a closed mesh to a solid. Autocad has some rudimentary ability but if your dealing with thousands of faces it will be a problem.
I use FormZ (not cheap) and it does a pretty god job, plus it exports to ACIS .sat files for Autocad.
good luck, let us know if you have more issues.