User blog comment:SsVivid/Monetary Reference Table/@comment-4536066-20130820055911/@comment-4835297-20130820122847

I think an adamant sword could pass of as costing a bit more than 2k. If you've got a bar of refined adamant for 1k, I think the price would be a bit more than double if it's used to turn it into a sword. Making that sword also requires the labor of a very skilled blacksmith, leather, an whatever else he smith'd use on the hilt.

Plus in Betrayal of Falador, we see that knights who are often around steel suits of armour are almost amazed to find a sword made of adamant. I think that sword was a bit fancier and dwarven made, but it seems a bit cheaper if its around the same price as two sets of steel armour.