I'd suggest either a Deere setup (GPS receiver, screen, and ATU) or Ag Leader and all their components. They move easily if you have both machines or all machines wired for it already. Just move those main components or in Ag Leader's case get a switch kit. 

Both brands you'd have a device/motor that goes on the steering wheel or column and steers the wheel for you. Deere look for ATU 300, SF3000 or 6000 can be had very cheap now, and either a 2600 with AutoTrac activation or 2630 with AT on it. 2

Ag Leader you could go used and get an older system like OnTrac 3 and older monitor like Integra or Versa. Or go new and get InCommand and Steady steer for more $$$. 

Both have good factory support and dealer support, if you have either dealer nearby. Since you're starting out I'd suggest going with who you have good dealer support from.