8.5kg exchange bottle from Bunnings is $27.90.
Don't have retail/wholesale gas in the NT, but do have two freaking huge gas trains with a capacity of about 4Mt for Darwin LNG and 8.5Mt for Ichthys currently coming on line - all for export.
There also happens to be an onshore supply surplus driving the Jemena pipeline, and a little bit of fracking to come too.. about 257,000 PJ worth.
Victorians just have to pay the going rate.