Is the problem the tile, or what is under it?
A cracked tile is not, by itself, a leak. On a tile roof the waterproofing is the underlayment underneath; the tiles shed most of the rain and keep the sun off it. So the first question about broken tiles is whether water has reached the inside. If it has not, the job is the one priced here. If it has, the underlayment beneath has torn, slipped or aged out, and the tiles are the smaller problem.
This estimate assumes the simple case: a patch of broken tiles with sound underlayment around it. The crew lifts the surrounding tiles, patches the felt under the damaged area ($29 to $58), dresses any flashing it disturbed and relays the tiles. If the felt they uncover is brittle and cracking well beyond the repair, the patch will hold only as long as everything around it does.
Underlayment usually gives out long before the tile, and a roof that leaks in two or three places at once is saying so. The job to price then is a lift and relay, in which every tile comes up, new underlayment goes down and the same tiles go back: see roof underlayment replacement. Spot repairs on a roof in that state buy time, not a fix.
Why tiles crack
Clay and concrete tile is strong where it is supported and weak where it is not. A heel on the middle of a tile, or on the crown of a curved one, can snap it, so many broken tiles appear after someone was on the roof for another reason: a satellite dish, solar panels, an air conditioner, painting or gutter cleaning. If you can see a line of cracked tiles leading to a piece of equipment, that is usually the story.
The rest is impact and weather. Hail and falling branches crack tile from above, and storm damage across a slope may be an insurance matter (see storm damage repair). In cold climates, water soaked into porous tile freezes and splits it, and older concrete tile wears at the surface and grows more brittle with age.
The repair breaks tiles too. Lifting the courses around the damage strains the tiles and their fasteners, and some crack. The estimate orders spares for that reason, and a quote with no allowance for breakage tends to come back with an add-on.
What if the tile is no longer made?
Matching is often the hardest part of the job. Concrete tile makers retire profiles and colors, clay varies from batch to batch, and even a tile still in production looks different new than one that has weathered on your roof for years.
Tile roofers have a few ways around it. Salvage yards and some roofing suppliers stock used tile by profile, and a broken piece, or the maker's marks often molded into the underside, narrows the search. Where nothing matches, a common move is to borrow sound tiles from a slope nobody sees, such as the back of a garage, use them on the visible repair, and put the closest new tile where the mismatch will not show.
A scarce profile can cost more than the labor on a repair like this, and it is the line most likely to differ between quotes. If spare tiles from the original installation are sitting in a garage or attic, tell the roofer before they price the job.
What a proper repair looks like
A tile roofer steps on the lower part of each tile, where it rests on the course below, and keeps off unsupported middles and crowns; foam pads or walk boards spread the weight further. The broken tile comes out in pieces, its nails are cut or pulled, and the new tile slides into place and is held with a tile hook, wire, a screw or adhesive foam, because the course above now covers the spot where a nail would go. Neighboring tiles are then checked for slipping so the problem does not just move one course over.
A quote for this work should say how many tiles are being replaced and whether they are new or salvaged, how much underlayment is being patched, how the replacements will be fastened, whether the permit is included, and what warranty covers the repair. Caulk or roofing cement smeared over a cracked tile is a stopgap, not a repair, and shingles over tile are not an option at all: IRC section R908.3.1.1 does not allow a new roof to be laid over existing tile.