I haven't heard anyone saying that the cost of an Audax could be significantly reduced. Personally I think it could, but then people won't bother to do them, as they would be glorified club rides, just you have to travel further to do one... what's the incentive, if you remove the brevet card, the points system and all of that?
The camaraderie? Well, to be frank, 90% of the time I am no my own.
If the price is right, then it comes down to individual circumstances.
The initial post asked whether Audax have become more expensive... I don't think they have, not beyond inflation... what used to cost 5, now costs 7 and what used to cost 7 now costs 10.
That is a far cry from the inflation cycling events in general have seen: take "The Eroica", which I entered in 2005 for 10 Euro, in 2006 for 15, in 2011 for 40 Euro and now it costs 70.
Or other forms of entertainment... take the 6 nations rugby. In 2007 I went to Dublin and paid 25 Euro for a ticket. In 2008 I went to Murrayfield and paid 40 pounds for a ticket, in 2009 I went to Cardiff and paid 60 pounds for a ticket... in 2010 I wanted to go to Twickenham and they wanted 120 pounds... I drew a line there and then.