Simplified RTK for newb

I am very new to ardupilot and drone building in general so forgive me for asking such a basic question.

I am interested in building (most likely someone else will do the building) a drone with a highly accurate GPS. My research is leading me down the road to an RTK GPS capable drone. what i require is a drone which can fly from one way point to another stopping along the way at pre determined positions. (if someone really wants to know why i need this they can contact me privately)

I want to put it out there to all the people who have experience with a RTK capable drone.

1.Whats your favorite RTK GPS module?
2.What accuracy should i expect? (i require cm accuracy)
3.what is the reliability of RTK GPS
4.What should i be paying for a drone? (i dont have much experience and dont want to get ripped off)

i would appreciate anyone who has advice for me on this subject and would like to thank the ardupilot community in advance. i have already learned a lot just reading this forum.