Courier compnay contract rates

Hi

I currently send roughly 30 parcels a week which weight just below 6kg. Im using interparcel.com at the moment but want to open a contract with a courier, i have contacted a few already (DHL, Citylink, Sendex) and am waiting on them to get back. What sort of price should i be looking at for this many parcels? and who else should i try? (im just about to give TNT a call aswell)

And any other general pointers are much appreciated.

Thanks
Simon