If the beading is on the inside they are a doddle to change, when I have done mine I paid 35 quid sq m for standard glass units. 28mm
have a try with this matey http://www.thephonebook.bt.com/publ...uble+glazing+repairs&TownOrPostcode=Barnsley# hope you get it sorted.
We have stopped swapping the glass units at work instead we use a company called Crystal clear who will come and basically vacuum out the condensation and replace the seal. They charge us fifty quid per glass unit repaired