How long is a piece of string - the cost could be any figure you can pick out the sky!!
The point is the extra cost of installing beacons or a pager system are seen as acceptable engineered measures in terms of the RRFSO and BS's - even though both methods are fallible - and if someone died the Centre Manager would have the defence that he had installed recognised and approved systems properly engineered blah blah blah ...here is the Certificate your honour please blame the designer.....
If he'd supplemented these acceptable measures with DMS then more power to his elbow.
If he only installed DMS then I don't think he could defend his position if he knowingly of unknowingly was relying on a signalling method he may have been mis-sold by his local electrician that is not recognised in any BS (presently) as the sole means of reliable emergency signalling.
