Which used model to buy?

[gps10]

I have a small project with plenty of space to mount a robot.  The application requires roughly:  x = 150mm y=100mm z=50mm.  I will perform about 600,000 cycles annually.  The cycle time can take as long as 3 seconds to run a variable path (always the same path) of about 18 inches.  Low accuracy and low speed are OK.  EOT = about 3KG.  Any suggestions on which model and what year to buy used for this project?  I would like a tried and true used robot.

Thanks.