The Ranges
For a typical project covering the unit, the venting, and a straightforward install, plan on roughly $4,700 to $6,600. Once finish work, a gas line, and electrical are in, a complete installation more often lands between $6,000 and $14,400 all in. On a remodel or a new build, a useful rule of thumb is about 2.5% of the total project budget.
What Moves the Number
Four things, mostly. How far the gas line has to travel. Whether there's an existing opening or a wall to frame. What the vent path looks like—this is the usual surprise. And how much tile or stone is going back on afterwards.
The One Question to Ask
Make sure any number you're given covers the whole scope: unit, vent, gas line, electrical, finish work, and the permit. You don't need a line-by-line breakdown and asking for one rarely helps. You need to know that nothing has been left out of the total.
What You Get Back
On average a fireplace returns roughly what you spent on it in home value. Add the running saving from heating the rooms you actually use instead of the whole house—commonly $20 to $60 a month—and the case is reasonable before you count what a fire does for how the room gets used.