It seems to paying for access to advanced workbench can be really nice idea but when you lost your reputation. First time, you should reach to 1000 points, and then you will be able to pay X caps for using workbench if you lost reputation. It is good idea because we have more options to choose - you can pay or do delivery quests if you do not want to pay caps.
In addition I would like to add new place with advanced workbench, for example in somewhere in dungeon quest. If you completed X dungeon quest you can have an access to this location for X time, after it location will disappear.