The cheapest I have found for Max thermostats is a company called alternate.co.uk. The small max wireless stat is today £12.99 but on top of that is £9.90 postage so they work out cheaper in quantity. I ordered a couple from them to test them out and they came through fine.
The annoying thing is that for some reason I do not understand they have a limit of 12 of any one item and I want 14 to complete the set for my new house. This is not a money limit, which I could understand, since I can order 12 x high end graphics card at £164 x 12, £1968 as well as my 12 Max. For some reason that they can't explain you can only order 12 and that's hard coded into their order system ::) Seems to me they haven't quite got the idea of selling......
Update: Found a solution.
Alternate offered to create an order for 14 stats to be paid via bank transfer but as I expected this was to a German bank so with the bank charges for international payments (even though payment was in GBP) this worked out the same as 2 lots of postage. I asked about paypal and they said they could do this but it would be in Euros. I tried this and there were no paypal fees other than paypal's conversion rate. I have a 0% fee credit card so I told paypal to pay it in Euros and used that. That's now ticked all the boxes, no extra postage, no bank fee, no conversion fee, so I'm a happy bunny :-).