We can't help you with the costs. Us guessing doesn't do you any good.
I'd suggest making a call to the local building inspection office to speak with an inspector regarding local/regional requirements for the vent termination. They'll more than likely tell you to follow the manufacturer's installation specs to the letter. Doors, windows, inside corners, overhangs and obstructions such as AC units or large bushes should always be avoided. The code sets minimums clearances, but I've found that the manufacturers are often more restrictive. The inspector should enforce the manufacturer's requirements or the code, whichever is more restrictive.