In America you can buy cans of Arctic Freeze for very cheap to re-gas your car aircon on the cheap
apparently it works really well
available here
http://www.ebay.com.au/itm/Arctic-Freeze-Ultra-Synthetic-R13…
unfortunately for some mundane reason its not available in Australia and the postage is somewhat prohibitive
but I found cans of CRC freeze spray available in Australia contain the same 134a gas
available here
http://www.ebay.com.au/itm/CRC-300G-FREEZE-SPRAY-CRC-2039CRC…
would this work if used like the artic freeze cans?
anyone have any ideas on making a suitable can to schrader valve adapter?
You're supposed to de-pressurize the system and do a few other things first, not just put some new gas in. I paid $120 to get it done properly and just buying a can and DIY without any equipment will result in a system which is not working optimally and which may not last as long before requiring another re-gas.