SOX lamps are becoming very expensive. In the days when SOX was pretty much the universal choice for local authorities, manufacturers and wholesalers had a good, stable market for their products. I recall that the lighting departments in my area were generally supplied through a purchasing consortium of several authorities. Buying in a greater bulk would achieve better savings in the cost of SOX lamps, than on a single purchase order from a single authority. Whether this continues now is unclear, especially with the PFIs etc.
The other situation now however, is that SOX is a threatened species hereabouts, therefore a manufacturer that finds itself gaining an increasing share of this diminishing market is unlikely to be sustainable in the long term.
At the end of the day, the price of lamps is based on their production run quantity - more output, cheaper price. Will LEDs go the same way?
Is the Philips factory in Scotland the only one in the world still making SOX lamps?