Where to buy big logs cheap?

I have this idea for garden furniture. You know how you can use a slice of log as a little stool? Well, I want to do something similar, but slice the edges of the log off, to make a little cube.
I rang round local tree surgeons last summer and one agreed to make them for �£10 each once he got some suitable wood.
I never heard from him again!
I have visited a woodyard and he said �£50 each (!) because of the amount of wood in them, but only �£20 each if I only wanted the round slices, not made into cubes (?)
�£10 each was about the level I was thinking of paying. The log needs to be about 27" diameter and about 72" long, and I need someone with a chainsaw who can do the work on them.
What else can I try?

 

are you sure of your measurements daisybelle.
Your talking 6ft x 2ft 3" square that's one hell of a lump.

 

Yes, I want them 18" cubes which I think is about the right size to make them comfortable to perch on.
Using the old pythagorus, I worked out you'd need 27" diameter to get an 18" square, and I want 4 of them, so that's 72" long.
Am I right in thinking, if you use a tree surgeon, the wood is just rubbish you're grateful they're getting rid of?
And yet in a wood yard, it's worth a fortune?