an NDB must be a very cheap thing to run
If you read the D&G thread referenced in the link above it refers to some AirServices Australia information
here (scroll down to item 6.2) which indicates that the cost of maintaining aging NDB installations is becoming prohibitive due to lack of spares and end-of-service-life issues. Replacement cost is estimated at AU$100,000 each (about £40k) according to this doc. Doesn't seem too much in isolation, but in Australia this appears to have led to the decision that it is not worth maintaining several hundred NDBs across the continent and the intention is to phase out most of these. (I guess this is why NDBs at e.g. Sywell and Compton Abbas are NOTAM'd as U/S forever... too expensive to maintain and capex not available to replace!?)...
If interested in ADS-B, there is another AirServices Australia link which explains the programme for this in Australia here:
http://www.airservicesaustralia.com/.../adsb/adsb.htm
Andy