There are some reasonable prices here, based on the retail price. http://store.apple.com/uk/browse/home/specialdeals/mac
Hypothetically, if I were interested in this one (http://store.apple.com/uk/product/FC309B/A), could I replace the hard drive myself, with a higher capacity one, or are they all sealed like iPhones, etc?
I think with the iMac the answer is no, you would add Thunderbolt or firewire HDD for data storage.
As I suspected - thanks, Steve.