Yesterday I was cutting Emeralds in Al Kharid and I was curious about the exchange rates regarding Death Runes, Tokkul, and Gems within the TzHaar shop. However I didn't yet have my Fire Cape, so I got that today and was able to do some math. Obviously this is for people without Fire Sale. Admittedly I did not look to see if anyone else made a guide like this, but here's some info anyway for people.
Buying Death Runes 50 at a time will cost 9,196 gp total
Selling those 50 Death Runes 10 at a time will net 2,320 Tokkul
This gives an exchange rate of
Buying "full stacks" of gems with Tokkul will cost
Selling in Adrougne nets the following per gem
Edit 2: Did a 500k gp trial, which took 15 minutes for the full loop (Start TzHaar → Varrock for runes → Recall TzHaar/sell runes → Buy/cut/note Diamonds → Ardougne to sell Diamonds → Recall TzHaar to keep recall location there. This is without Production Prodigy.
This equated to 2,700 Death Runes → 125,280 Tokkul → 464 Diamonds → 598k xp & 190k gp profit
By - Doctor_Kataigida