While I am generally for community-based things, I think this could cause more problems than it solves. Especially if the problem is market competition - speaking as a seller, the market is plenty competitive
Put another way, like the enthusiasm for the market (woo market), really don't like this idea! (sorry not sorry)
When I started selling I made a spreadsheet like what you've described. Where it is, whose it is, what they sell, whether it's in stock and for how much. Never shared it - partly because the formatting is awful, but anyway.
Potential/likely problems:
-Keeping it up to date. Back then the market had ~300 priced chests. That's 300+ chests to be monitored and updated for prices/stock, as well as any more chests that get added anywhere. Maybe the shop owners will keep it updated, maybe not.
-Keeping sellers happy. However the 'data' is ordered, it will cause issues. If you order it by shop, someone's name has to go first. If you order it by goods, someone's name has to go first. That will irk the people whose names do not go first.. If you order it by price, you actively encourage undercutting.
-It makes undercutting much easier to do. It happens anyway, but with a spreadsheet people can work out how to gut prices in a second. This will annoy people.
And by people I mean meI think that a general 'guide' of the market may be useful - not having prices, but showing where different shops are and where you can go to get things...but even that would crop up with the same potential issues.