bulk purchases are sometimes tricky on exex since its based on supply and demand. the price can creep up rapidly if there is a low supply of them so the first 100 may be around 3000 and the next 100 around 3500 and the next 100 around 5000 (this is just an example) thus you dont risk the downside risk of the price going up dramatically. also you dont pay a commission. it's nice to have people selling bulk items even though they are on exex, makes life simpler sometimes.