The only ways I would know to get this information would require reversing knowledge.

First being writing something to read process memory and iterating/dumping item prices from the menu - Not sure if BE runs/scans on the menu but if so high chance of being banned.

Second would be reversing the menu traffic as the menu communicates with a web API to get data, which is how market bots work. Once this is done you can easily just send a request to access trader inventory the same way the game does and it returns everything you'd need.

Both against tos and bannable, the second option though only gets people banned if they send unusual traffic/spam requests.