I have no practical experience in this whatsoever. However, as happens
when a topic comes up, information sometimes pops itself into your life
quite unexpectedly. In this case, at the weekend parked at the top of
our road in London was a van for UPakWeShip.com, who I'd never heard of
before. I've just had a look at their web site. They offer the range
of services you might expect, from excess luggage, through crates right
up to containers part-load or full. What's useful is that they give
some prices up-front.
I now know that a 20-foot container from New York to London with them
is $3500 (under $3 per cubic foot), and that a shared container for the
same trip is about $11 per cubic foot. In neither case is collection
or delivery included, these costs are purely the shipping. A more
domestic service is a box 56" x 39" x 39" (50 cubic feet) collected and
delivered for $999 ($20 per cubic foot).
There are of course plenty of other such operations, many no doubt
cheaper, but anyway it's interesting to put some figures to these