I have no problem allowing players to spend 100g to have a "masterwork" weapon.
It's the mechanical bonus I take issue with.
With plusses to hit and damage capped at 3, it's difficult to find space for how to differentiate a high quality weapon or armor. In my campaign, the players picked up some expensive half plate that reduced the sneak penalty to -1 instead of disadvantage. It's also very fancy-looking.
What stats do you mechanically give a masterwork weapon? "Expand your crit range by one. E.g., if you currently need a 19-20 for a critical hit, you now need an 18-20. If you roll the lower number on the range, roll a d10 and on a 1-2 (or whatever) you critically hit." This would add a small 1% chance to crit, but most players would find it valuable enough they'd probably want one.