Didn't read all the comments but did anyone mention a Jetta GLI? Seems like it fits all the criteria; comes in manual or auto and, with as much as you are willing to spend, you can get the top of the line model (and still be way under budget).
EDIT: In my personal opinion (I can't stress this enough) there is a certain stigma attached to BMW/Mercedes owners as well. I can completely understand your concerns about making a good impression to perspective clients. I would also assume your "clients" would include potential investors as well as state/local government officials? I think you would want a nice, clean vehicle which is well maintained and "middle class." As opposed to a vehicle which could be viewed as a status symbol. Where I come from (suburban Houston, Texas) and where I am now (active duty military) BMWs, Mercedes, and to a lesser extent Volvos are most definitely viewed as a status symbol.