The biggest obsticle to us installing much root barrier or moisture barrier is that you have to buy 50m rolls, and frankly we have never had enough demand up here.....they'll cut the tree out rather than install root barrier!
However when we were trying to develop an interest in our clients up here this company stood out
http://www.rootology.com.au/index.php really switched on and abreast of tree biology and the limitations of using barriers.
In Qld this company has pretty much cornered the market
http://www.rootbarrier.com.au/ and these guys in Victoria are possibly another option for you
http://www.treemax.com.au/landscape/rootwall.html. Depending on the situation and the client this is a good option for some Councils or larger developers
http://www.reclaim.com.au/gen_pro/flexipath.html.
Prices certainly will have changed since we were interested (2yrs back) but our invisaged costs generally started around $35 per metre installed up to almost $50, depending on the site soil access etc...