In the meantime ... I've been thinking about a slightly different hive for awhile now ..
The Zest Hive was what started me off thinking ...
http://thezesthive.com/
But I reckon that you could make a 'Dartington' using lightweight insulation blocks
http://www.wickes.co.uk/Wickes-Aerated-Block-3-6-N-100mm/p/213632
So ... the lighweight blocks are 440mm long x 215mm high.
A standard national frame is 356mm wide in the frame part plus say 14mm in total to give you bee space at either side = 370mm. And, guess what, a standard national frame is 215mm high including the thickness of the lugs so sitting them on top of the blocks would give you bottom bee space. You would need to cut the end blocks down from 440mm to 370mm length but that's the only two cuts to make.
These lightweight blocks are easy to cut with an old saw if needs be.
Therefore you could make the walls of a Long Deep Hive - 3 blocks long and one (cut down) block wide for the princely sum of 8 x £1.79. (I'll do the maths - £14.32).
The blocks are 100mm wide and so they would sit on a simple frame made out of old fence posts. Or new ones if you don't have any lying around (having just replaced 6 with concrete posts I have some ...)
http://www.wickes.co.uk/Wickes-Timber-Fence-Post-100mmx100mmx2-7m/p/548025
With a mesh floor held in place between the timber posts and the lightweight blocks.
http://www.ebay.co.uk/itm/2X-VARROA...782?pt=LH_DefaultDomain_3&hash=item2a3db07c5e
It would need a crown board and a roof of some sort with insulation in it - perhaps pallet timber for the roof.
But, I reckon you could have 'Dartington style Zest type' Hive in place that would have the internal dimensions 370mm wide x 215mm deep x 1120mm long for the following costs:
Blocks £14.32
Mesh floor £10.99
Post £12.79
I've assumed the other bits will be scavenged. Need a bit of paint for the outside and perhaps a batten to go round the blocks at the top to keep the frames in place but let's say a tenner for the odds and sods.
Less than £50 for a hive that will take 30 standard national frames, highly insulated and with all the benefits of a Long Deep Hive ... Clearly it's not going to be a hive that can be moved but long hives are not really intended for mobility.