In our own experience "certified by 3M, PPAI, Avery, whatever" they charge no more than any other contract installer. That being said there is no hard per SF price. The cost all depends on the job you want them to do - many factors affect that with the actual amount of material being only 1 small part. Install conditions (climate controlled indoor, outdoors, etc), distance they ware going to have to travel, what exactly it is they will be putting vinyl on (trailer, trailer with 9000 doors on it, full wrap van, full wrap VW Beetle - Beetle, quarter the material, just as long of an install as the van, graphics on walls, etc, etc), the type of vinyl plays a large role - laminated 3M versus some no-name crap material that might be an aggressive nightmare to work with might take twice as long to install, being nice and cool with them on the phone versus being a pr!@k, etc, etc, etc. ALL of that greatly affects the cost of an install.