Fixed mounts are stationary. Those that move with the sun are called trackers. Trackers are all pole top mounts.
Photovoltaic Mounting Systems, Solar Module Racking
Roof mounts are the most cost effective and are priced according to how much wind/snow load they can withstand. The greater the load requirements, the greater the cost. Ground mounts are made for structures without adequate roof space and are more cost effective than pole mounts.
Costs vary greatly by region (and even by zip code). To get free estimates from local contractors, please indicate yours.