When farming ore, in a lot of cases it will be sold as bars instead of ore. It would be convenient having the price of bars (or the most expensive currently between ore and bar?) instead of ore.

Hmm, that's an interesting idea, though I'm not sure how I would go about it. However, if you want an easy and already available solution, you can track the bars by adding them through the custom filters.

Tracking bars that way works - when you're smelting, not when you're out mining, which is what would be interesting for me. A way to approach this could be a user-configurable section of mask items - an item ID A is masking item ID B, you track collection of A but display information about B. I'm not familiar enough with WoW add-on development to know whether that's actually feasible though...

That is a decent idea, and certainly possible.

Also, as for tracking the bars. You can use the option to show all filters, which shows any selected filters, even if you currently have 0 of that item in your bags. Just have to be more selective with which filters you select.