Ice - Diamonds are very specialist merchandise and you could end up with anything. My grandmother used to describe it as "buying a pig on a poke" which I think sprang from the old market tradition where you never judged the contents of a shut sack by just 'poking' it; you opened it to see if what was claimed was actually inside.
Why not get a budget-airline flight to London and visit the Hatton Garden (diamond centre) shops to see what the range/prices are. The "West End" and traders such as Cartier are much more expensive. Amsterdam is probably the cheapest and best place in Europe for purchasing diamonds and you could try googling De Beer.