a) Dryers are very simple beasts. So simple that more-or-less anyone familiar with the operation of basic hand tools who understands basic electrical precautions, and knows enough to take many pictures during the disassembly operation to aid the re-assembly is qualified to make basic repairs.
b) A repair person will charge anywhere from $75 - $150 to walk in the door, and then any parts on top of that. And as igniter repairs require considerable disassembly, probably another hour in labor.
c) If the machine is 20+ years old, it may need replacement anyway, so a visual inspection by you prior to making any repairs and/or expending any payments on outside labor or parts would be a good thing.

And, if you do decide to make repairs, replace the drum gasket, bearing and rollers as well. Doing that + the igniter makes the dryer "practically new" but for the motor - and those seem to go very nearly forever in my direct experience.

Look all this up on You-Tube, there will be many such repairs shown, probably one for your specific brand and type of dryer.

Peter Wieck
Melrose Park, PA