so... if it that simple and cheap, why need freighters? Because that makes every solar systems become self sufficient. Replicator could render every economy rules that we know now useless. Plus, the non currency life in Federation makes Merchant obsoletes. So why we still have the freighter captain Yates in DS9? Why they still transporting goods from one place to another? Because it is no longer necessary, if Replicator is indeed the machine of god. They don't need freighters, Merchants, distributors, etc anymore. Everyone could make their own item with the "replicator". and everyone could take the energy from their own solar system.
So... unless replicator is not that powerful just like you state, replicator is just a bad idea that come from bad writing of those lazy writers.
So even in a replicator society, there will be a need for freightors, just what cargo goes in the freightors will be a little different.
Here is a list of some potential cargo:
1) Food Items:
- Naturally pre made food or basic food items ready to be cooked with for those on the frontier where replicators are not ready / installed.
- Pre-replicated food for helping hungry people
2) Medical items:
- Biomaterial used in labs for creating medicine and other biological items since biomaterial isn't replicatable.
- Medicine for helping others.
- Artificially grown biological body parts for helping the injured.
3) Personal mail
4) Living creatures or plants
5) Handcrafted items
6) Manufacturing equipment:
- Raw matter
- Batteries / Generators
- Pre replicated tools
- Construction Equipment
7) Parts for a giant power plant or other buildings.
8) Equipment for specialty application that can’t be replicated easily.
9) Custom made small vehicles
10) Any non replicateable raw material
All because you have a replicator society, doesn't mean you don't need cargo transports, it just means what you transport becomes more specific to the needs of a ever expanding society.