If money really isn't an issue you should think about a LION unit.By and large,most forces use LION products.The 500B being a popular (handheld) unit.They do need regular calibration to remain effective and this may cause you issues as calibration can be a bit convoluted and requires further,specialised equipment.Accuracy drops without calibration and to avoid errors,the 500 has a 30 day window before recalibration is required.
Another manufacturer is Dragër-also used by Police forces.
Both are obviously,very accurate,but the latter has a longer time between re-calibration.
I believe that both companies sell to the public,so check out their sites.
I have no knowledge of cheap devices advertised on the Internet.