Much like many things in solar, there’s a wide variance from one item to the next. It’s also important to note that there are many components in addition to the panels that are needed for a properly functioning system (Inverter, Racking, Hardware, Permits, etc). That being said, a typical solar PV panel is about 3.5 feet by 5.5 feet, covers approximately 18-19 sq./ft., weighs around 45 pounds and is rated at 250—345 watts and will cost between $200 to $550 depending on quality and efficiency.  Overall system cost can ROUGHLY be translated to $3/watt for a residential system.  Typically a bit higher for a smaller system, and lower for a larger system.