Presumably they blew off? My other house had a problem with the ridge shingles blowing off and after paying and seeing how the first ones were replaced I simply nailed them back on myself when the others came off. In my case the builder had nailed them in with the air gun cranked up too high so the nails went right through the shingles and into the ridge vent.
Just nail them back down and cover any exposed nails with roofing sealant.
If it was from the wind, replace the entire ridge.
Depending on the orientation of the house, start on East end and finish on the West end, or start on the North end and finish on the South end.
If it just a couple feet of cap shingles you would be better off doing it yourself, unless its a big & steep house. That is truly the easiest part of a roof you can do. No since in paying $200-300 to have it repaired, unless you just physically can't get on the roof. You don't even really need to match the color perfect.....since you cant see cap shingles much from ground.