This came through my email today (no direct link, as its instore only - of course!)
I personally prefer to have my bottles filled rather than swap'n'go as I know the quality of my bottle and that its been stored under my BBQ.
The cheapest I've found in Canberra for a refill is $25, but I know a few places on NSW North Coast that are about the same price.
Masters usually has cheaper empty gas bottles (if you're in Canberra, there's a Rays next door to Masters at Majura).
EDIT: Credit to Sween64, who got a Swap'n'go for $23 - available where Rays don't go gas fills
http://files.ozbargain.com.au/upload/84851/26842/image.jpg
The BCFs also do refills, my local one is normally $19.99, but it ranges from store to store. Also watch out when buying a gas bottle, cheaper ones are often grade 1 and more expensive ones are grade 2