Window quotes look like they are about windows. They are mostly about openings.
Insert versus full frame
This is the largest single cost variable, and it is decided by the condition of what is already there.
An insert window fits inside the existing frame. It is faster, cheaper, and leaves the exterior largely undisturbed. It requires that the frame and sill are sound and dry.
Full-frame replacement removes everything back to the rough opening. It costs considerably more, disturbs siding and trim, and takes longer. It also allows proper flashing and a sill pan to be installed, which is the difference between a window that manages water and one that hides a problem.
In older Washington housing, full frame is frequently the correct answer rather than an upsell. A contractor recommending it after inspecting the sill is being straight with you; one recommending it without looking is not.
Condition of the opening
Rot at the sill or in the surrounding framing is the most common cost escalation in Western Washington window work. Decades of marine damp against openings built without sill pans produces it reliably.
Ask what happens if rot is found once the old window is out. You want that answer before the wall is open, not while a crew is standing in your living room.
Size, shape and operation
Standard rectangular openings cost least. Bays, bows, arches, large fixed panes and anything non-standard cost more, sometimes considerably. Large glass is heavier, needs more people to install, and costs more to replace if damaged.
Siding and trim restoration
Full-frame replacement disturbs the exterior, and putting it back is real work. Matching existing siding — particularly on older homes where the original product is no longer made — can be a meaningful line item.
This is a common gap between quotes. One contractor prices restoration properly; another leaves it vague and addresses it later.
Glazing package
Low-E coatings, gas fill and triple glazing each add cost with different payback. The right answer differs across the state: solar control coatings matter most in the Tri-Cities and Yakima where summer heat gain is the problem, while insulating performance matters more in Spokane where winter cold drives discomfort.
Energy code
Washington’s requirements exceed the national baseline, so replacement units will typically be a specification step up from what came out — particularly in growth-era homes fitted with builder-grade glazing. That is a requirement rather than an upsell, and a contractor quoting below current standards is quoting something that cannot be installed.
Phasing
Replacing in stages is entirely reasonable and spreads cost, though you may lose some volume pricing. Prioritise the worst-affected elevations — usually south and west facing, and anything showing rot or failed seals.