Fair questions
Can I try a plunger or a hand auger first?
On a single slow fixture, sure, and plenty of people fix it that way. Where we would say stop: if the lowest fixtures in the house are backing up, that is a main line and a plunger will not reach it. Forcing it can push waste into places you do not want it.
Why is my clog back so quickly?
Usually because a cable opened a channel through the blockage rather than removing it, so the remaining grease or scale narrowed it again. Or because the real problem is roots or a break, which no amount of clearing fixes.
Do you charge more for a main line than a sink?
They are different jobs with different equipment and access, so yes, they price differently. What you will not get is a sink price on the phone and a main line price at the door: that is why we ask which fixtures are affected before dispatch.