Question from a newbye

Hi there,
In my company, we are looking for a commercial product able to deal with
Autocad files. We mainly need to display image on Web browser, and
eventually to add small object to them. We used to work with 2D building
plans, but now our client need 3D representation of their building. So we
have to deal also with that aspect: migrate smoothly from 2D towards 3D.
We are looking for something cheaper that Auocad with Windows API/SDK.
If you have any idea, please let me know !!
Oriane