Best way to figure out the value is to start from there, but I would say about 10-11k would be a good bet for the chest. Just as a small note there's a lot of people who have stocked up on the Scarlet pieces
I can't speak for the others, but my Scarlet Chests are left over from long ago, when it was the only one of the set that had any value (IIRC the drop rate was quite low, and only from one boss in Scarlet Monastery).
I think I used to buy at 5g and sell at 15
It's nice to know it's still worth something though - I can use it as a "sweetener" if I ever sell something valuable to an RP player or 'mogger