The best way to match up monitors without visual difference is for all the monitors to be of the same make, model, and revision. However, even this will not guarantee all monitors will look the same due to minor variations in the manufacturing process.
Yer gonna have to manually tweak whatever monitors you buy to make them all look as close to each other as possible. The amount of time it takes to do this will depend on how exact you want it. It can take several minutes to a few hours and even then it will not be 100% perfect.
If you don't have a monitor calibration tool. Windows have a program that allows you to calibrate the monitors with your eyes. It won't be accurate like a real calibration tool but you should get the monitors to look the same.