If you are looking at the Mamiya TLR's, another option is the Koni Omega 6x7 rangefinders. I am using one as my main landscape camera. A body, back or two, with 58/90/180 lenses seems to be going for less than $500 on ebay. I don't know what the availability is in the UK. It and the Mamiya C series are probably the most cost effective ways to get a wide angle lens in MF. Close focusing is not the KO's strong suit, but that may not be a problem with the landscapes you shoot. It is also hand holdable, with the side benefit of being a left arm weightlifting program Seriously, I've gotten some quite respectable hand held photos with it at 1/30 - I'm not sure you could say that about the Pentax 67, from what I have read about it.

Jon