It really depends what you will be repairing, and to what degree.
You might get by with a VOM, soldering tool, and a number of screwdrivers and pliers, and such.
To get more advanced, you would need an oscilloscope, maybe an function generator, adjustable power supply, RF generator, specific generators/monitors for things line video and radio equipment, SMD desoldering/soldering tools, jigs and stuff to run boards out-of-situ.
Not to mention a parts stock, documentation, furniture you will need, a computer with access to service info, and sometimes directly needed to service some equipment with test/programming interface/software, and of course a place to actually run your business from.
Prices can vary. Sometimes with proprietary gear, they soak you, other stuff you can get used, and sometimes make yourself, or use off the shelf retail devices.