Try www.shiply.com
Its the e-bay for couriers. I've used them for a few different times for shipping large items.
Basically they are commercial couriers who are picking up parcels and packages, which can be delivered on their return journeys. Its worked well for me in the past, and has been very cheap.
If your selling your item on eBay its really easy as the two sites are integrated. Just input your item number, and couriers respond in a few hours with their quotes. You just pick and accept one.