Just buy a new RD and have the bike's shifting properly set up.
I've set up and worked on a handful of Claris drivetrains and its a simple setup.
If you want a new drivetrain, cool, its always fun to get new stuff.
Nobody knows how much money it'll cost because we don't know your budget or what sort of drivetrain you want.
- spend $300 or 1500?
- 2x or 1x?
- Cable disc or Hydraulic disc?
- Shimano, SRAM, or Microshift?