Timing sets the price
Flashing beside a wall or a dormer is not laid on top of the roof. It is interleaved with it. A piece of step flashing goes down, a shingle covers it, the next piece sits on that shingle, and the pattern climbs the wall course by course. When the old roof has been torn off, this costs the crew very little extra, because they are laying those shingles anyway. That is the job priced here.
Putting the same flashing into a finished roof is a different job. Every shingle along the wall has to be lifted, its seal strip broken, the new pieces slid in and the shingles nailed back without cracking them. Per foot it takes much longer, which is why repairing flashing on an existing roof costs more per foot than new flashing on a new roof.
So if a wall is leaking and the roof is within a few years of replacement anyway, a modest patch now and full new flashing with the new shingles is usually the cheaper path.
The details that decide whether it leaks
Where a roof runs up the side of a wall, the flashing should be separate L-shaped pieces, one per shingle course, each a little longer than the exposed part of the shingle so it overlaps the piece below. Some crews bend one long strip along the wall instead. It looks tidy and goes on faster, but it has no laps, so water running sideways across the roof finds the joint behind it. On a sloping wall a continuous strip is a defect, not a shortcut.
At the foot of that wall, where the roof edge stops but the wall keeps going (a garage roof against a two-story wall is the usual case), the last piece needs to be a kick-out: a small angled diverter that throws the water out into the gutter. Without it, everything that ran down the step flashing pours behind the siding at the eave. The result is rot inside the wall, found years later and often well below the roof. Kick-outs are small, usually bought preformed, and frequently left out.
Above the steps, something has to stop water getting behind their top edge. On a sided wall that is the house wrap and siding lapping down over the flashing. On brick, a separate counter flashing is let into a groove in the mortar, the same work covered under chimney flashing repair. Where the siding was cut tight to the old roof, a course may need to come off to fit new flashing properly.
Choosing the metal
The estimate prices aluminum coil, $111 to $157 for enough 10-inch roll to cover the length with a cutting allowance. Aluminum cuts with snips, bends by hand or on a brake, and does not rust, so it is the default on most asphalt shingle roofs. Its weakness is contact. Wet mortar and concrete are alkaline and corrode it, and so do the copper-based preservatives in modern pressure-treated lumber, so it is the wrong metal against brick or treated wood unless something separates them.
Galvanized steel is the other everyday choice, stiffer than aluminum and in a similar price band. The zinc coating protects it until a cut edge or a deep scratch exposes the steel, so it tends to rust first at the cuts.
Copper costs far more per foot and can outlast several roofs. It is soldered at its joints rather than sealed, and it is common on chimneys, valleys and older houses. It must not touch aluminum or galvanized metal, and that includes the gutters downhill: water running off copper corrodes them. The roof flashing guide compares the less common metals too.
What to look for on the quote
This figure is flashing only. Shingles, underlayment, tear-off and disposal sit in the roof replacement price, and the shingle calculator covers those. Also outside it: drip edge along the eaves and rakes, which comes as preformed sticks and usually gets its own line; pipe boots; and the flashing for a skylight that is being replaced at the same time, which comes as a kit matched to the new unit.
On a re-roof quote, look for the word "new" next to flashing. Reusing the existing step flashing is a common way to trim a bid, and while counter flashing that sits in a sound groove in the brick can sometimes be bent up and reused, rusted or bent steps carry the weak points of the old roof straight into the new one. Ask for kick-out flashing by name, and ask whether step flashing goes in piece by piece.