I got a couple (different sizes) from Ronnie Sunshines when they first started stocking them. As it says in the small print, you have to do the seasoning yourself (the more expensive brands eg Lodge come ready seasoned).
The biggest cost with these things is the p&p, I managed to find myself within a short diversion of berkhampstead and so arranged to collect.
Good guys, good gear, reasonable prices (no links, just a satisfied customer).
As previously stated, they don't stay in stock long and they know they're already very reasonably priced, so I doubt they'd do much of a discount for a GB unless it was for large numbers, and as stated a good proportion of the cost is the shipping.
On a similar note, anyone know a cheap source for good potjie's?