There are many factors that can affect the cost of an automated gate.
The type of gate that you have installed is a large factor.
The cheapest type of security gate is a basic chain link swing or slide gate. The most expensive type of gate is an artistic double swing gate made of steel with hand painted accouterments.
The type of gate opener you have installed is another large factor. Typically electro-mechanical 12v DC powered gate openers are the cheapest, and hydraulic openers are the most expensive.
Furthermore, whether your gate automation system is installed as a basic push to open/push to close system, or has vehicle detection devices, safety devices, voice communication, keypads, card readers, and cameras installed is another factor affecting price.