There is no single answer here. The answer strongly depends on several factors. You can easily check yourself and then decide.

The mechanics is excellent in all modern diffractometers. What changes is:

- configuration: do you need a theta/theta or theta/2theta, horizontal/vertical? traditional or benchtop?

- detectors: are you happy with a scintillator or a proportional counter or do you need a high performance or a 2D detector? This is the major issue and depends on the type of measurement you want to do, the materials you analyze

- specs: but that seems not your problem

- software: some machines come with extremely powerful and rich software.. ask what's included and compare. You don't want to spend $10000 extra to buy the software that was not bundled with the machine (there can be extra costs per year if your main target is phase id and you want a high quality database)

- after sale service: this is 90% of your machine. Ask people in your region and see who's providing the best service for the money. I think you can survive with a slower detector or a missing feature, but if the machine gets broken, you want it repaired immediately and with no surprises about costs.

This includes also the cost of the X-ray tubes that you have to replace regularly if you heavily use the machine.. and tubes don't come for free!

Ask ALWAYS for some test measurements on a machine analogous to the one you want to buy (and if possible be there and see..), to avoid surprises.

Good luck! Choosing a diffractometer can take a long time, believe me

Thanks Matteo! Very useful comments.