Every realm has different prices
At least the more popular realms have lots of mining bots posting stuff and they rarely smelt the ore into bars. Sure the obsidium prospectors need a boatload of ores everyday, but there's still more gold to be made if more of the ores were turned into bars.
Currently it costs less than 2g to make a bar and bars go for 3g. From my experience during weekends the prices are lower and during peak hours they are usually even higher, but obsidium ore stays low almost everytime. In other words, there's a lot of profit to be made!
- Use 12 hour duration when posting bars. You will get undercut and the fees are often high!
- You need 425 skill in mining to make use of this.
- Try other ores aswell. Copper, Bronze, Cobalt and Saronite often have even higher profits!