http://online.wsj.com/article/SB10001424127887323777204578195470446855466.html
Wall Street Journal says the cost of australia's new gun bans was $500 mill (Us Dollars)
as to the second assertion, the above cited source puts "Gun Homicide" reducing by 3.2% (a shitty ROI) but increase in the criminal use of illegal unregistered weapons is up significantly (stats not given)
further, homicides in general are down 9%, and armed robbery down 33% (not bad) but (uhh ohhh!) assaults are up 40% and sexual assault is up 20%.
to me this speaks of two associated issues:
1: killing the other guy is no longer so easy, for both the perp, and the victim
BUT....
2: those with criminal intent now feel more secure of their safety in their endeavours and are hard at work doin what criminals do, in what has become, for them, a much safer "workplace"
personally i would much rather see more dead perps getting their chalk outlines sketched, and fewer crimes in toto.