Daki,
Have a look in the Classifieds sections of the following kayak fishing sites: www.kfdu.com.au www.akff.net www.bfo.com.au . Otherwise keep looking at EBay and Trading Post online (www.tradingpost.com.au) as well as the Weekend Shopper. $500 aint a lot of cash - you won't get much for that. But then again you never know. Good luck.
Cheers,
Pete