The installation cost for a gas fireplace is more than the price upfront, as it depends on the following factors:
Does a unit require a separate construction or it’s an insert?
Do you have an existing gas line or you need a new connection?
Whether the unit requires the construction of a chimney or it’s an unvented fireplace.
This shows that your overall installation cost can range from around a minimum $500 to $2500 or more.