I visited this guy yesterday who is selling off his massive collection of tricho pachanoi (I think they're pachanoi) The gumtree ad is here

http://melbourne.gumtree.com.au/c-Stuff-for-Sale-homeware-furniture-outdoor-backyard-bbq-Cactus-SanPedro-W0QQAdIdZ182325527

The 30-40 cm ones are $15 and there are various larger clumps from $20-30, it is well worth having a look if you want some mature specimens. A couple were unhealthy but there were some nice fat green ones. I won't put his number here but you can email him through gumtree

That looks like some good value. I'm looking for some landscaping plants, so I may have to fire off an e-mail or two...