You can buy 50 dragonstones every 4 hours, which is a total of 2.5m considering dragonstones are around 50k each. 50*50 = 2500 = 2.5M.
You buy uncut dragonstones from the GE.
You go to the Tzhaar gem store.
You sell uncut dragonstones to the gem store
You buy the uncut dragonstones from the gem store for roughly 900 tokkul each.
You can either then keep the dragonstones, or sell the dragonstones back to the guy so you get PLAIN CASH (and don't have to sell the dragonstones back to GE) and you repeat every 4 hours.
In order to get tokkul, i suggest you sell Chaos Runes to the Tzhaar rune store - this results in you losing 1M for every 5M transferred i believe.
Very simple calculations to work out how much you'd lose would be;
Each uncut dragonstone is 900 tokkul each, it costs 50k.
Each Chaos Rune is 45-90 tokkul (i can't remember excact), they cost 150GP.
If we say it's 90 tokkul, you need 100 chaos runes for it. = 15K.
If we say it's 45 tokkul, you need 200 chaos runes for it. = 30K.
Each Dragonstone = 50k.
50 - 15 = 35.
50-30 = 20.
So it is an efficient way to transfer without risks.
Hope this helped.